Reason 1 Fallback If an athlete does end up becoming pro, they can get injured and end their sports career. So, it is good to have some education to get a backup job.
Reason 2 Maturity: These athletes may not be mature enough. If they're 17/18 and they've won a game, these kids are going to go back to the hotel and play games rather than going with the pros to the club and party.