You know, maybe if you prioritized getting a really good script before shooting the movie, you wouldn't have to keep reworking the thing. Scripts are cheap, it costs practically nothing to just keep working on them until you have something really smart and creative.
Or you could slap something together based on the studio roadmap and notes from marketing, because it's all just a placeholder and half of it will be replaced in post production when they decide what they want the movie to actually be. Why pay a good writer or two when you can work an entire vfx studio half to death trying to crunch their way through to the release date?