Well, a large problem is that players in guilds had to leave their guild, this created a lot of problems since some players didn't want to leave their guild and rejoin, also guild leaders had to leave temporarily to reassign the guild leader.
You also had some AFK problems and we would suffer from delays from thinning out MCs.
Using a scripted NPC to randomly distribute players would not be as 'balanced' as hand selecting because you have the probability that player skill would be distributed unevenly. Also, if they NPC is accessible multiple times, a player can leave and rejoin until they are in a 'good' team.
So, it is more of a hardcore event that requires a lot of patience and obedience, which are limited resources =P


