What Hook said. I'll add that sometimes, a draft is nice in that you don't have to pay attention constantly for 3 hours. Mainly, though, it's that the majority of FF players are less sophisticated that what you see on this board, and an auction is too complicated. That, and auctioning in person is tougher than a draft.
I have to chuckle at the auction folks who think dynasty and IDP leagues are somehow "less sophisticated". These types of leagues are plenty sophisticated. 40 man rosters with IDP is probably more "sophisticated" than an offense only auction. That is, if the defensive scoring system is strong enough to start taking stud LB's in the 4th and 5th rounds of a redraft and there are 9 IDP starters.
I get a kick out of "How the world should work" opinions. Thankfully, simple redrafts, keeper leagues, dynasty, IDP and auctions are all out there. Each has it's own appeal... and it's own shortcomings. No one system is intristically better than any other.