Like most others I thought you were thinking of Tebow. It is ineresting tha you weren't.
Even if a schools academic standards aren't the highest, there is still a lot of time a student must dedicate to attending classes and at least passing. On top of that, I would guess that the programs have not only a pretty full calendar but also likely have restrictions on what their athletes can do outside of practice. My guess is that there is simply not enough time to allow for developing college and pro skills simultaneously.
It is the same in any endeavor. Why doesn't a great lawyer also get his CPA because he can make more money with both titles?
Rich or poor, black or white, we all have only 24 hours a day.