This moves the advertisement opportunity to the chat owner. If you want to use chat (+api) to book a table at a restaurant, then the reservation-api company loses a change to advertise to you vs. if you used a dedicated reservation-web-app.
Oh I see what you mean, yes. The reservation api company will have to get money through other means (either from the user via OpenAI or from the restaurant).
Honestly I see this as a positive change, I'd rather be the customer than the product.