Directing has changed, too. I used to know a B-list Hollywood director. Directors used to come from a theater background. Theatrical directors make a script work by walking through it on a bare stage and making changes until it works. This doesn't work in films with lots of effects. If you try that on an effects film, you go way over budget. Which has happened more than once.

Big movies are now waterfall projects - everything is preplanned. As one ILM guy said, a Star Wars movie is three years of preproduction, three months of principal photography, and three years of postproduction. Movie directors now are more like animation directors - they storyboard, they plan, they previsualize, they have a full previz version created, and only then do they get the green light for full production. Upper management gets to see all this work, so there's more interference from above.