Disney lawyers > director’s guild lawyers
Don’t forget the DGA made a big stink and fined George over putting Kershner’s name at the end of ESB. (They somehow overlooked Lucas doing it to himself on Star Wars.) Lucas quit the DGA and the pool of director’s he could hire from for Jedi was limited by that. Probably one reason Spielberg never directed an episode.
Lucas was independent enough that he could make films outside the Hollywood system, but Disney isn’t.