To be honest, he needed to stay in Brooklyn. No other situation would have made him championship level happy.
Also,
The Rudy Gobert to Minnesota trade has broken the league for future superstar trades. Minnesota gave up FOUR first round picks AND 5 players (including this years' 1st round pick) just for Gobert, so these teams (Brooklyn) arent gonna accept less for a better player like Durant, AND if you traded all that from your team, there is nothing to play with and win.
This is why these Durant and Donovan Mitchell trades have not happened (although with the Knicks front office, anything can happen)