Talented players are encouraged by their AAU programs to stay back in 7th or 8th grade. This makes them stand out in tournaments, because they have typically matured physically versus the kids they are playing against. This also draws the attention of high level prep schools.

Fast forward to junior year. They are receiving scholarship offers from P5 schools; they are already a year older than their class. If you're staying on top of your classes, most juniors have almost enough credits to qualify for graduation, or can finish up with a few summer classes. So now the player moves back forward to his original class.

Does it make sense ... no. But a lot of AAU and recruiting doesn't.