Would you agree they don't need to consciously stick to it, because that structure is internalized already as "the best way to write a mainstream movie"?
Not that I entirely disagree with you, but I think it's more analogous to say that Hollywood is in the business of making burgers. You expect certain structural elements in burgers: buns, centre, sauce. They're incredibly popular for a reason.
The problem comes when we say burgers are basically the superset of decent or nutritious cooking.