It's also why Google doesn't want to just charge for services. I wouldn't pay more than about $60 a year or so, because I am very much on the low end for value I bring to Google, but they would never accept that because it would be a huge haircut on the high value users, and if they set it high enough to be profitable for high value users, I literally can't afford it.

The ad ecosystem allows them the equivalent of ideal price discrimination. You bring in exactly how much revenue they can squeeze out of the economy for access to your eyeballs.