In the doc he says he didn't want to do it anymore once he turned pro and it became a job. I don't know how much of that statement is compensation for not being good enough and how much of it is a valid reason. He also fell back on having a bipolar diagnosis, which didn't appear to hamper his ability in college.
The doc wasn't very informative regarding perceptions of other teammates and people around him except for the OC and his agent, and his one-time best friend.
The NFL had him pegged though.