There are actually significnatly fewer writers today than in the heyday of scripted television, when seasons were 24 episodes long and nearly every hour of prime-time was scripted television.

As for ChatGPT: ChatGPT is not competent at writing substance. ChatGPT excels at superficial basic structure; the kind you learn on the first day of high school English. Those who have tried using ChatGPT to write fiction have discovered that every story follows the same simple pattern, and it always skips over the most important part of the story (i.e., the part that writers would actually need help with) to skip straight to the conclusion where everybody lives happily ever after.

So ChatGPT might help a student with the bones of their creative writing assignment. But it and its LLM ilk will never be a force in Hollywood; that would require a better type of AI that is actually capable of substantive understanding.