We are, are we? You must be a lost member of RTRPE.

They are there to stop the war between Carthage and Egypt which never happened in reality but was a nightmare in RTW and RTR 6/RTRPE. And it makes Carthage to expand rather in the westward direction as it did and concentrate on Iberia and Rome. It also gives Egypt more chances against the seleucids.
The other one is there to stop Bactria to go north each game and expand rather ahistorically. The problem was that instead of concentrating more on the seleucids it was going north into poor and mutinous regions where it was loosing money and troops. These are the reasons we did it like that. Of course, there is an optional with its own installer that takes out the land blocks. Easy as that.
PS: how come the equally artificial landbridges didn`t bother you?