Because he felt Duke had a better shot and getting him into the NBA than BYU did. And he was correct about that. Probably because Duke is seen as a program who has better access to scouts and NBA networking than BYU.
If Payton Dastrup stayed with Ohio State, I doubt he'd be averaging 8 MPG. There's no reason he shouldn't be playing over Worthington and Seljaas right now. Program absolutely matters as far developing these kids to be drafted and giving them proper access to be seen by scouts.