Google pays to be the default search because they make more from selling ads on those searches than they are paying for the search.

I don't see the same thing here. Google isn't making any money from being the assistant in Apple, so why would they pay to be it?

Maybe. Search ads likely make Google more money than they pay apple. For AI, Google currently loses money. If they eventually make money via ads, then sure. Else, apple will have to pay them

Search has ads but Siri doesn't. And when Apple puts ads in Siri they won't be Google ads. I don't think Google benefits from this deal enough to be worth paying.

Eventually? I bet they already are.