Mapu, GC, and KICEMEN actually bring up very good points about not allowing CYOC (even if they didn't intend to). There are 3 potential problem situations:
First: Let us say a noob starts a brand new CYOC game on the world map. Selects Central States just for fun. Logs out, and comes back a day later to find the game has started, but he's surrounded by bozo, Ruffhaus, myself, and Ambassador. Kinda sucks for the noob that he has literally no chance to win because we were able to pick to surround a weak player right? And even if the noob were used as a pawn and survived the early game, they'd have no chance in the long run. Something like this would very rarely happen in random draw.
Second: Player A creates a CYOC game. Player B comes along and realizes that Player A, who is someone he almost always gets along with and can usually ally with, has an open slot next to him. So Player B grabs it, knowing that he has a good shot at allying with this player right from the start. This gives an advantage to people who know each other in that they can pick slots where they can *usually* (not I'm not saying always) have an assured ally nearby whereas new players (who dont' know many people) can not. Again, something that random draw would prevent from happening. At least in random draw, if those players are next to each other, it's due to "luck", and not because they were able to choose it to benefit themselves.
Third: Player A is ready to join a CYOC game. He notices Amby, bozo, Ruffhaus, and myself are all in North America. Realizing that to join there would mean a very difficult start to the game, and that Africa has a bunch of newer players in it, Player A goes and joins Africa so he can dominate the noobs. Player B comes along, and the only slot left is in N. America. How is it fair that just because Player A joined first, he has the option to avoid the good players if he wants, whereas the last player to join is stuck with whatever spot is left, even if it means being surrounded by the best players on the site? It's not.
I don't expect this to convince anyone, but you can't deny that these are distinct possibilities that would unfairly influence the balance of the game, and that they're all easily avoidable by random draw.