I read a few answers but did not see two major factors mentioned. The rise of mass media created celebrity culture, which empowered actors vs studio executives

I read a few answers but did not see two major factors mentioned. The rise of mass media created celebrity culture, which empowered actors vs studio executives. This gave actors more say on how movies are made, and naturally, they made changes that make their work look better. Another major factor was the rise of improvisation as a recognized, legitimate, and valuable style of acting. In the old days the Script Was God in the studio system; actors did what they were told. The rise of auteur directors, and then celebrity actors, created room for directors and actors to invent lines and whole scenes on their own. This helps things seem more natural, and it allows productions to efficiently work around script problems that were not caught in pre-production.