I don't see how suddenly hundreds of billions of additional ad revenue will appear.

I think some of AI companies truly wanted to make a fortune replacing all white collar workers through model exclusivity, but that open models (initially Llama and then a sequence of really good Chinese models) threw a wrench in the cogs. There is not as much you can make anymore if everyone can host their own 'workers' near cost price.

But LLMs do have some niche, stable applications already. For example, they replaced Stack Overflow to a large extent, because you can get the answer you need faster, and it's often better adapted to your situation. So you could argue the novelty of SO wore off a long time ago but people were still using it when LLMs appeared. ChatGPT is no more en vogue, people are ashamed to (and shamed for) using it, but it still has some uses, helping people in their jobs and lives in general.