People click on irrelevant ads. It doesn't cost them anything.

I bid on "seating plan" for my seating planner software in Adwords and lots of people searching for "747 seating plan" and similar clicked on my ads, despite the ads clearly being nothing to do with that. (I fixed with with setting "747", "a320" etc as negative keywords).

I don't think this is sufficient to account for the terrible engagement from ChatGPT ads though, unless the targetting is just garbage.