I'm not so sure. Inserting ads into chatbot output is like inserting ads into email. People are more reluctant to tolerate that than web or YouTube ads (which are hated already).
If they insert stealth ads, then after the third sponsored bad restaurant suggestion people will stop using that feature, too.
Mmm let's see. I think in LLM ads are probably have the most intent (and therefore most value) of any ads. They are like search PPC ads on steroids as you have even more context of what the user is actually looking for.
Hell they could even just add affiliate tracking to links (and not change any of the ranking based on it) and probably make enough money to cover a lot of the inference for free users.