They probably want to have enough people to fill in any demographic holes they get when they figure out what their class is going to look like. Still, I agree that it's ridiculous to have 3 levels of waitlist or 800 people on a waitlist for a 250-person class, but I think that many schools also feel bad rejecting people so they just put them on a waitlist instead. W&M tends to do that both at the LS and UG levels.