Starting over every year is a personal choice. Cal takes great pride in the number of players that he sends to the NBA even if some are not ready and end up in the D league. If he took the time to develop some of his "regular" players, maybe he would have players on his teams that could act as the glue to keep his teams together while his young 5 stars learning how to play the game.
Some leave early because they play up to and over their potential and others too early and it blows up in their face - Dakari on this roster dramatically changes the dynamics.