I played basketball in college many moons ago, at a level well below Kentucky. I mention that because I have a theory about Alex that I'll admit would have applied to me. I'd played basketball all my life to get a scholarship, and battled through lots of injuries in both high school and college. By the time I was a senior in college, I was burned out on hoops and much more interested in getting on with my post-educational life.
Of course, I didn't have the prospect of making millions of dollars in the NBA or Europe, but maybe Alex has come to realize he's not really an NBA-caliber player, and he's just ready for the rest of his life to begin. Maybe this is a feeling that has grown for awhile, but he's kept it at bay as he fought back from last year's injury because part of him realizes how privileged he is to be at Kentucky as a basketball player. Internal conflicts are not that uncommon, especially among intelligent 21-year-olds. By all accounts he's a great kid and an excellent student. If so, good luck to him.
It's easy for people whose careers topped out in junior high to say, 'man, if that were me I'd be running through brick walls to play for Kentucky.' I'm not doubting anyone who feels that way. But the reality can be more complicated.