Problem is people come in to try the game (alot of kids this time of year) and are all excited and play a ton until the newness wears off, then they re-roll when they have a clue and go to another guild on the new toon, and never log in on the old messed up one in your big guild.
Just hard to tell who is going to turn into dead weight, and who isn't until they do in fact become a drain on renown.