I agree it is a problem, but how exactly would you enact a solution?
Imagine the NCAA trying to pass a rule that Colleges are prohibited form hiring AAU coaches? Any chance that could be legal?
So try to address it from the player side. Can the NCAA prohibit a player from going to a college that happens to have a coach on staff who had coached them in AAU? Even if this reach is possible, what if the timing is flipped.? If the player signs then the coach is hired, can the NCAA force the school to renege on the scholarship offer?
Again, I'm not missing the problem, but the solution isn't jumping out at me.