With one of the main goals of every college football player being to get to the NFL, it's come to where the best of the best tend to spend as little time in school as necessary before setting off on a pro career. Though they can play four seasons and attend class for up to five, once three years are in the books many will make the move to the NFL.
Sticking around and using up every bit of eligibility has somehow become a red mark when evaluating a player's talent level, the feeling being that if they were good enough to turn pro earlier they would have done so.