Further: if you have Damian Lillard for example, why would you have a backup for him about as good. ? You are now creating a player controversy at that position. Would you expect the ,Cavs to get Durant to back up James and only play them each for 20-30 minutes a game? Or would you change one of their positions and play both? What point is there to having two guys that do the same thing on the court at same time too? Don't you want guys that do different things to change up the rhythm?
You are using real world logic which does not apply to the situation at hand. And from a real world standpoint it would probably not succeed there either. Football it would make sense to have backups almost as good.
Baseball/basketball it makes less sense. It makes more sense to either teach different positions or play different positions to get the lineup as well, or to trade/move them to clear salary space.
But that's what a manager does not a coach. So maybe you just do better at coaching than managing and that is a communication breakdown within your front office?