James is a unique player. He has to have the ball, and sometimes behaves like a one man team. While it's true that he can pretty much do anything he wants on the court with the ball, his play often is not conducive to team play. The other guys just stand around while he does his thing.
If a team is established and has a certain chemistry, it may be tough to adjust to him. There would have to be changes made, and some coaches may not like that. GS had no problem making Durant work, so maybe James can work elsewhere, too.
Another consideration is his age. At 34, he is going to slide soon.