Durant and Kyrie can go to Brooklyn and turn them into a contender without much help.

Mahomes and Hill could go to the NYJ and they’d barely make the playoffs at best.

In short, a star NFL player doesn’t make his team good by himself. You need a lot of good players to be good in the NFL. NBA, not so much if you have a few great players. This leads to a lot of roster turnover and most teams have to rebuild every few years. That at least seems to be part of it.