The cost of LLM inference is orders of magnitude more than the typical ad CPM.

Not even "native ads" embedded in LLM output can offset the difference.

ChatGPT is way above typical CPM, maybe $60-$100. That puts it in the same category as premium YT verticals. If they can sell enough at this price point it would make a big impact, but I'm super-doubtful they can do that; campaigns are basically blind at this stage, and I would not be surprised if this was intentional.