Your willingness to pay makes you a more attractive target for advertisers. Something newspapers figured out about right after the printing press. If their oral predecessors didn't tell them.
Discussion
Thats why the likes of Google never really put up a fight with the ad blocking industry. It's only lately that they try to be more strict about blocking ads.
I've asked where this is ad coming from in a follow up question. This ad placed not by OpenAI, but from the plug-in vendor. Doesn't make it less annoying though.