pete carroll tried to do the same thing with sanchez. basically the argument is qbs who go earlier are less likely to succeed in the nfl (which the stats apparently back up). i think it's a garbage argument since i refuse to believe that a year in the nfl wouldnt' be better than a year in college, but apparently this works on some guys. locker is very raw. much more so than sanchez, but he'd be stupid to not take the money and run.
Maybe he loves College Football. Maybe he thinks he can develop more playing next year rather than holding a clip board. Who knows, but you can get an insurance policy to hedge your risk of injury. It does't cover all the money you could lose, but it certainly can cover a nice portion of it.