The reasons why Georgia and Bosnia aren't included is back when I was first making this mod they weren't included (I didn't include a lot of factions for various reasons). As the mod progressed and I hit the faction limits it became harder and harder to add these factions into the campaigns, especially when I had other factions I could add that didn't require me to make any new units, banners, symbols, etc.
One major problem is that if I add a faction to some campaigns that have a free faction slot but not to other campaigns because they don't have a free slot the faction seems to disappear for no reason. For example if I was to add faction B to the 1200 and 1400 campaigns because I have a free slot but not to the 1300 campaign because I don't have a free slot then it looks like this faction ceased to exist in 1300 and I'll get a lot of people asking me why I didn't include it. This isn't a major problems but from a continuity perspective it looks odd.
So if I can't add a factions to all the campaigns it should be in it's often easier to add it to some of them and use another faction in other campaigns, so I could faction G in 1200 and faction B in 1400, then claim that G had declined by 1400 and that B was more important in 1400 to hide these difficulties.