Saying that AIs will never write a good movie is like saying AIs will never generate a beautiful image. If anyone has used Midjourney or Dalle-2 they know that these systems are very capable. However, they were trained on material that was often under copyright without the permission of the artists.
This also happened with Co-Pilot training on computer code written by humans who didn't always consent.
It will be somewhat different for Hollywood studios since they own the copyright to literally thousands of produced and unproduced screenplays that will be used for training. And we should expect those screenplays to be used to train the next batch of AIs to generate very good screenplays.
There will still be humans in the loop, but a single human will be able to generate a massive number of screenplays using AIs. You can imagine giving an AI screenwriter the basic story points and getting a finished script in 30 seconds.
It will definitely change the nature of screenwriting, but it won't replace writers in the short term. However, in the long term these systems will evolve and potentially be able to write compelling screenplays with all the nuance and subtlety of a seasoned human writer.
But before everyone starts to think the studios are in the driver's seat, in the future these systems will be able to generate the entire movie including the actors, music, and everything else. At that point the studios will be replaced — which is something they're probably not factoring into their analysis.
Netflix displaced Blockbuster video, and generative AIs will displace the