It doesn't work like that. The NBA is basically a boys club, controlled by their bylaws, and to become a member of the club, you sign off certain rights. For example, one of such rule is that the commissioner decisions are final, and you forfeit your right to sue over those decisions. Furthermore, IIRC, the bylaws include a clause for mandatory arbitration, which is pretty common in this kind of agreements.
This whole thing plays out in contract law. Cubes would have to first sue to declare the bylaws illegal, potentially risking his membership and sending the league on a spin. He's not going to do that.
EDIT: That was one of Sterling's original claims, that the bylaws were anti-compe ive. Which, IIRC, was dismissed.