Maybe he's got an alpha mentality and wants to improve by going against the best of the best every day in practice and hopes that Cal can help him with the defensive part of his game (as well as marketing him after his playing career at UK is over). Maybe he wants to play on a team that he knows is going to win a lot of games and doesn't mind a more limited role than he'd get elsewhere. Not every players thought process about choosing where they want to play is going to be the same. There's plenty of reasons as to why he'd want to come off the bench here.