Villanova recruited him as well and they have other recruits riding the bench. His high school coach told him he wouldn't be playing at Villanova either. The 2021- 2022 season was the closest to how freshman were used before the one and done trend of the last 15 years. That is because of super seniors. It was clear to me that Diggins physically wasn't ready to play and was a liability when he was on the court. The future for him will require maturing physically and putting in the work. He sees the writing on the wall. He may be ready next year but he may not be either and the following year there is a player coming in that he knows he will not beat out as starter. Probably a good move for him. He is not the answer for next year and most likely would not want to be a backup his junior and senior years, although that may be his role no matter where he ends up. Sampson Johnson will be an impact player before his career is over but needs to develop as well. He may be ready to contribute next year if he can get stronger over the summer.
Your pick one request is wrong as your choices are wrong. Developing a player doesn't mean throwing them in a game when they are not ready. It means telling them what they need to improve on to get to play and helping them to do it. If a player thinks he is ready and he is not, then the worst thing a coach could do is reinforce his delusion by playing him anyway. An opportunity goes both ways. When Calhoun was coach there were many players who left the program who thought they were better than the coach's assessment of their abilities. Where they all his failures or was it the player's unwillingness to accept their role? I don't know because I was not at practice and don't know the individuals and who was advising them. Neither do you in the present situation.
You start off your choices with "what wrong with our guy" That presupposes that the only explanation for a player not being ready to play in the Big East their freshman year is the coach's fault. Maybe he overestimated the kid's ability but maybe there are other reasons as well. I don't expect recruiting to be perfect it is a two way street. I wish the best for Diggins in his career and hopefully his departure will allow another player to come in who is a better fit.