Some off-the-cuff, half-baked thoughts from my sick bed:
AAU, et al. takes the tribalism out of sports and just makes it an activity.
There are all kinds of personal benefit from sport for the athletes. But the reason, I think, sports are so big in the world is because of the tribal aspect. And I think playing for your tribe or gaining prestige through playing for your tribe are benefits most athletes would enjoy.
Tribalism can be a bad thing, obviously. But if tempered, it brings a sense of belonging and identity that human beings naturally crave.
Doing the AAU, non-tribal route, then, involves a trade-off for each athlete on multiple vectors that must be measured by each person.