These examples might also be due to collaborative pressure.
On Star Wars, Lucas worked with a great editor who could say no to him. Same for script on Empire. For the Star Wars films 1-3 Lucas had total control over everything.
Put another way: It's commercial pressure that made Lucas subject to collaboration. And it's subsequent commercial pressure that made collaborators subject to Lucas.
Compare old Star Wars to new Star Wars.
Or The Matrix to its hypothetical sequels.