Parent is presumably making the case (and I'm assuming this extends to their respective ad pricing models) that it's revenue equivalent but profitable either way.

Either you have intent but little attention (Google et al.) and so can charge a decent amount.

Or you have lots of attention but little intent (Facebook et al.) and so can charge a decent amount.

You can't charge a decent amount if you have little intent and little attention.

OpenAI presumably has intent, but hasn't done all the Google-esque adtech sausage making to expose that to ad space buyers.