Why almost all infantry prefer spear than sword?

[Satrio Eko]

just look at yourself,almost all infantry in the game for all faction (except magadha) using spear as their main weapon,why not sword?

[AqD]

Because technically swords were very difficult to make. 60cm+ or 75cm+ would be considered long and expensive (even gladius was long by ancient standard), most soldiers in ROP times can only afford knife-sized swords, which are not too useful.

[Blatta Optima Maxima]

Because swords have nearly always been sidearms, that is, secondary weapons. In a mass battle, they aren't all that useful. Even in the late medieval period, men-at-arms preferred polearms as primary weapons, only using swords as back-up. Note that most soldiers of this period had some sword as a sidearm, which kind of topples aqd's point.

[AqD]

Because swords have nearly always been sidearms, that is, secondary weapons. In a mass battle, they aren't all that useful. Even in the late medieval period, men-at-arms preferred polearms as primary weapons, only using swords as back-up. Note that most soldiers of this period had some sword as a sidearm, which kind of topples aqd's point.

H,mm you skipped a lot of part on Romans, Iberians, Gallic Celts, Indians, and some greeks too. The sidearms you mention are more like knives or extreme short swords like xiphos, which are not useful and never become primary weapon for next thousands of years. Also medieval european style of fighting is merely a tiny part of military history.

What became one of the primary weapons are normal-length swords or longswords, at least as long as early Gladius, Falcata, Khanda etc. They were not easy to make until tech advanced, back in Achaemenid times only the very rich and noble ones could afford (ex: Kopis, used by Persian cavalry too), and after everything fell in medieval europe, old Spatha which once owned by every Roman cavalrymen somehow became precious weapons again.

[TWWolfe]

H,mm you skipped a lot of part on Romans, Iberians, Gallic Celts, Indians, and some greeks too. The sidearms you mention are more like knives or extreme short swords like xiphos, which are not useful and never become primary weapon for next thousands of years. Also medieval european style of fighting is merely a tiny part of military history.

What became one of the primary weapons are normal-length swords or longswords, at least as long as early Gladius, Falcata, Khanda etc. They were not easy to make until tech advanced, back in Achaemenid times only the very rich and noble ones could afford (ex: Kopis, used by Persian cavalry too), and after everything fell in medieval europe, old Spatha which once owned by every Roman cavalrymen somehow became precious weapons again.

And Even feudal era knights, the kind we always picture using a sword, would only use them in very specific circumstances. They would use maces, axes, the lance, daggers, name a weapon, it was likely that a knight would have wielded it at one time or another.

[Blatta Optima Maxima]

H,mm you skipped a lot of part on Romans, Iberians, Gallic Celts, Indians, and some greeks too. The sidearms you mention are more like knives or extreme short swords like xiphos, which are not useful and never become primary weapon for next thousands of years. Also medieval european style of fighting is merely a tiny part of military history.

What became one of the primary weapons are normal-length swords or longswords, at least as long as early Gladius, Falcata, Khanda etc. They were not easy to make until tech advanced, back in Achaemenid times only the very rich and noble ones could afford (ex: Kopis, used by Persian cavalry too), and after everything fell in medieval europe, old Spatha which once owned by every Roman cavalrymen somehow became precious weapons again.

The kopis, a 60cm or larger falchion type sword, was used by the Persian infantry as well. It just took a back seat to the spear and the bow.

And as said above, even knights used swords as back-up weapons. On foot they generally fought with spears or axes.

[General Sultan V]

This is'n a prefference, Swords have always been reserved for the most worthy of them, even Then spears are rampant, Because they are easier to manufacture And Mass Produce and They most importantly Came first. For thousands of years the spear has been the main arm For many militaries, Excluding a few Armies, such as the roman army, possibly the best in history

[Blatta Optima Maxima]

So knights couldn't afford swords?

BTW, by the late middle ages, pretty much everyone had some form of sword, yet there were very few people who used swords as primary weapons.

[General Sultan V]

no, Swords were restricted to those who either deserve or Can Afford them. Most levy/Conscript/Line Troops of many medieval Armies were armed with spears, such as the famous spear walls of Hastings. An example of a Typical medieval battle where both armies used spears as their main infantry-of-the Line weapons. Expensive weapons such as Axes and swords were weilded by huscarls and wealthy knights, most of which were personally purchased

[Sir Walter]

Swords were (and still are in many armed forces' dress uniforms) a massive sign of status, hence their figuring in heroic myths (Fergus' rainbow sword, Excalibur, etc.) because they were incredibly expensive to make well - especially in the ROP time period. Obviously technology improved over time, making them more common by the Middle Ages. Also, the cheap swords used as sidearms were closer to being daggers and were far from ubiquitous, and were nowhere near as effective as high-quality longswords like the Roman cavalry spatha, derived from the Gallic style used by their nobility. There are very few legendary axes largely because they were thought of as mundane weapons by comparison, not because they were any less effective.

[Satrio Eko]

But in medieval 2 some infantry use shorter sword than knight sword

[Satapatiš]

Because spears are easier and quicker to produce, easier to use without extensive training and are easily replaceable. Not to mention that spears provides troops with more tactical flexibility whether we are speaking about cavalry, or infantry.
Sword, long knive or cutlass (in fact in the Medieval times majority of infantry "swords" were rather a kind long knives with one cutting edge, like this one) in battle was warriors weapon of last resort, when he expended all arrows, throwing spears, or his thrusting spear was broken. Or when close combat formation was broken and every warrior was fighting on his own. Each of these situations was not very desired in general.
Also, keep in mind that in the RoP time frame most units aren't professional warriors. And even a few of professional troops are issued with their weapons by state - the cheapest is weapon, the better. Babylonian army is a good example, though they were issued with basic swords.
Then there is a matter of training. Most of RoP troops are levies. These men have everyday diuties, jobs and families and not a lot of time for an extensive training - this is true especially with Greeks. Not every hoplite was really trained with sword, many of them doesn't even carried swords.
Spears are far easier for use, especially in larger groups of soldiers. It's easier to attack or defend yourself with large shield in one hand, and spear in another (and it's even easier to attack from horseback with spear, than with relatively short sword).
And the last is matter of tactics. Large group od men armed with long spears are very effective both in attack and in defense. They don't need to have a lot of training, it's enough if they know how to march in more or less tight formation and are disciplined enough to keep their place on the battlefield.
In short - spear, especially paired with a shield -is your everyday "noob friendly weapon". Good for conscripts, good for professionals, cheap, and even if it's lost or broken you can easily find another one.

[Satrio Eko]

So,the sword that used by Armed Sowrdsman Unit in M2TW are long knives?
anyway.thanks for everyone for answering my question

[Blatta Optima Maxima]

no, Swords were restricted to those who either deserve or Can Afford them. Most levy/Conscript/Line Troops of many medieval Armies were armed with spears, such as the famous spear walls of Hastings. An example of a Typical medieval battle where both armies used spears as their main infantry-of-the Line weapons. Expensive weapons such as Axes and swords were weilded by huscarls and wealthy knights, most of which were personally purchased

Levy =/= conscript. Levied troops were serving under obligation, not against their will. Most levies had their own equipment. At Hastings the Anglo-Saxon shieldwall was like that, a levy of freemen. They were all reasonably well equipped. Many lacked swords, but all had a sidearm in the form of an axe or a saex (something resembling a very short falchion/big meat cleaver). But you're just recounting one stereotype after another.

Let me make this clear: at Agnicourt, pretty much everyone, on both sides, had a sword. But very, very few people used it as a primary weapon. Most had axes, spears, halberds, maces, hammers, or whatever other type of weapon for fighting. And that's including the archers, mind you.

@Satapatiš Falchions are swords.

BTW, in the end none of this is relevant, because we KNOW that Persians carried swords. It's attested to in Greek sources.

[Satapatiš]

So,the sword that used by Armed Sowrdsman Unit in M2TW are long knives?
anyway.thanks for everyone for answering my question

Actually, it's an engine limitations and playability reasons that units in TW games are armed in standarised fashion.
Ideally in your average primary meele unit some men should be fighting with swords, some with axes, maces or even clubs, and some with long knives - though don't be fooled by this "long knive/great knive" name. What is called Medieval long/great knive could have blade as lon as full sized sword. And even two-handed great "knives" were known.
Ideally only troops explicitly known for fighting with certain weaponry, like the Varangian Guard or landsknechts, should be armed in more or less standard way.
But such realism not only would be resorce consuming, as it would end with greatly different soldiers animations and models inside every one unit on the battlefield, but also very dull from a gameplay point of view - there would be only generic two-handed/one-handed/spear units differentiated only by troops skins and quality, with and occasional exotic elite unit.

[Blatta Optima Maxima]

Just because the Germans ironically called their greatswords "big knives", doesn't mean they weren't swords.

[Satapatiš]

Just because the Germans ironically called their greatswords "big knives", doesn't mean they weren't swords.

This is a rather interesting case of semantics, wthat is a "sword". There were court trials in the Medieval period between sword makers and knive makers guilds, in which knive makers were accused of breaking sword makers monopoly for making swords - because they were selling one edged weapons shaped like knives but with blades as long as one or two-handed swords.
One of such weapons, basically a very long two-handed cleaver with one sided blade is even on exposition in local museum.
Personally, I'm not that touchy on the details and I would count any blade capable of cutting and thrusting as sword, but if we are going too far that way it breeds risk of counting even saxes and scimitars as swords.

BTW, in the end none of this is relevant, because we KNOW that Persians carried swords. It's attested to in Greek sources.

Greek swords, akinakes and whatnot, but I believe that OP question was why swords weren't primary weapons.

Also, I can't concur with theory that blade weapons were THAT expensive or difficult to make. Technology was known since bronze period and iron is much more common than bronze (or rather metals needed for making bronze alloy), also iron is much more durable more than bronze except problems with rust. This makes iron sword cheaper and more durable weapon than bronze one and we know that swords weren't uncommon in the bronze ages.
Akinakes is iron weapon and was quite common - certainly not a sign of exclusiveness.

[Blatta Optima Maxima]

Not "Greek sword", kopis. No reason to assume it's Greek, or non-Greek, or whatever. It's a falchion, and common everywhere. The Akinakes is not a sword, though, but a dagger - and Greek vases never show those. Neither do Greek sources mention them. Spears were inexpensive, but the main reason they were used by everyone is because in a shieldwall they are more useful. Greeks used spears too, even though they could obviously afford swords.

[Satapatiš]

Actually, akinakes is described as "sword" "short sword" or "sword-like" as well as "dagger" so if it qualify for being sword or dagger depends only from length of particular example.
There is one Greek ceramic depicting Persian with akinakes and there are men armed with this blade on Persepolis reliefs. Given these depictions and fact that it was used by iranian peoples we know that Persians were using akinakes, what we don't know - how often.
Do they were using mainly mesopotamian or iranian weapons and Greek vases were depicting them with other blades because such weapons were more familiar for artist, or vases were completely accurate and kopis was indeed more common?

Spoiler Alert, click show to read: 

[Blatta Optima Maxima]

While the vases might not be completely accurate, the kopis was common everywhere. The Phoenicians used it, the Egyptians (apparently) used it, the Italics used it, the Iberians used it. Why not Persians?