Maybe. But then:
1) Durant seems obsessed with winning. He genuinely thinks that he is the best player in the world. He won't ever be rated as good as James, but he has a good chance of ending with more rings, more finals MVP and more points scored than James. That seems important for him.
2) By being in such a great team, he can prolong his career. He needs to spend less energy, he doesn't need to be at 100% every game. Longer he plays, more money he gets, better legacy he leaves behind. Durant cares about his legacy as much as James.
3) He seems to be loving it here, and is good friends with Steph and co, is having fun there. Heck, he can even coach there for a game if he wants to.
4) It is San Francisco, a great city to live.
5) Arguably more business opportunities than in any other city in the world.
I mean, New York with Porzingis and potentially Kyrie sounds good, but why settle for some good when you are already in a great place.