Because it has to happen too much on the down low to be outright bidding. I've heard plenty of stories about how coaches get around the rules though...no idea how true this is, but one of the things I heard was that Julio Jones was roommates with a walkon who also happened to be the son of a prominent booster. When Julio wanted cash, said son of booster would give him the debit card daddy set up for this, Julio would go withdraw cash, then do whatever he wanted to with it. The way it was related to me was that because it came from a teammate and fellow student, it's perfectly within NCAA guidelines...but I have no clue how true that is, either being within the guidelines or if it even happened.

However, that's just an example. I'm sure that everyone skirts the rules with such tricks. That was Bear Bryant's greatest strength, IMO. I know I'm in the minority of Auburn fans, but I don't believe he ever actually cheated, I just think he exploited every loophole there was to be found. Way I heard it from one old school fan was that he taught the NCAA how to cheat, because he was always one step ahead of them, but by the time other coaches caught up, the rules had been changed and the other school would get punished.