which team they play for. Whoever makes them the most famous makes them the richest.
There was a good article written on who these guys primary employer is. It is most certainly not the team or the NBA. It's all about sponsors and being famous.
I think Lebron has a 1 billion dollar deal with Nike. He could easily play for free if it meant winning more championships/being even more famous.
http://www.gq.com/story/lebron-james-nike-deal-bilion-maverick-carter