We lost Vaughn because his handler was offered big bucks for him to play at UNLV. Diallo was ours to lose, but Fred closed the door when he told him that he may not even be here next season.
Of course there's always a reason why we lose recruits, and each recruit is a unique situation, but my point is what you said could hold true for every 4/5 star that chooses a KU (or fill in the blank blue blood) over a school like ISU. For the most part, these recruits are interested in the NBA 10x more than they are becoming a college legend.