I think you grossly overestimate the accuracy of LLM-generated docs and underestimate how much time technical writers spend on tasks that aren't strictly "writing." Generating text is the easy part; gathering and verifying information is much more tedious, but arguably way more important.
And I have yet to encounter an LLM that can repeatedly poke an engineer or PM until they cough up the details you're after—let alone one that can do that without making an enemy out of that engineer or PM :P
LLMs produce a ton of garbage. The job is still relevant if you care about accuracy. Maybe LLMs or some future form of AI can do the job, but using LLMs today is ill-advised.
And I have yet to encounter an LLM that can repeatedly poke an engineer or PM until they cough up the details you're after—let alone one that can do that without making an enemy out of that engineer or PM :P