You're assuming the customers who want to advertise on ChatGPT will want it to look like the typical low quality internet ads, not like billboards or "company branding marketing", something I think is much more likely.
Instead of selling impressions/clicks, they'll sell "injections" that hopefully (from their PoV) at least has some impact, like a billboard or TV ad today.
However I'd still bet that OpenAI is gonna be hit with a multi-billion dollar fine from the EU within 5 years of rolling out this feature. And they will pay and move along. Just how big tech works these days.
(that said, big companies have proven to be very effective in disregarding laws anyway)
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