Due to anti-free enterprise and anti personal freedom rules which are the antithesis of American ideals.
It just so happened (or was it coincidental)that those rules had a negative economic impact primarily on African American athletes.
For contrast, why is it that tennis, golf, hockey and baseball athletes (also actors, musicians, welders, programmers, etc.) do not have to go to college at all before going pro.
What does going to college have to do with being a pro basketball player. Nothing! It's just free R&D for the NBA. In exchange, the NBA suppresses the labor market, allowing colleges to hold onto kids who could otherwise be off making more money than most adults.