I suspect that Riley has multiple issues and what has never been said about him can be more telling. It has never been said that he has a terrific work ethic, is a student of the game, very demanding of himself etc. I suspect that college football might be too much at the d1 level. Some kids just want to be kids. It has nothing to do with his god given physical ability. By all accounts, he is the most physically talented of the four.
I have a son that walked on at an fcs school and earned a starting spot his RS frosh season. After the season, the coaches talked to him about an expanded role the next year. Guess what? He quit.He was tired of playing and just wanted to be a student. He lived to regret the decision, but sometimes kids get sick of the level of commitment it takes to play.