The incredibly boring but true answer is: nothing of any substance. As pointed out downwind, yes, the data gets sold ... mostly to advertisers and ad platforms, on the promise it will somehow make ads even smarter and more effective.
As noted: it does not. And it is a huge problem for the entire industry and one that was rapidly coming to a head, before crypto, and then AI, came along and promised to save everyone. Now those are collapsing too and the tech industry is basically mid-crash right now, but like Wile E. Coyote, they haven't all realized they ran past the cliff about a mile back.
Mind you, some of them have, which is why the industry took MASSIVE layoffs across every part of it, as their stakeholders all panicked at once. They blamed it on COVID, but the reality is COVID didn't really hurt tech nearly as much as it claimed because how could it? How exactly is "everyone is at home all the time" gonna hurt companies whose business is literally all about keeping you glued to a computer or a TV or a smartphone? COVID was always irrelevant, but it gave them an excuse to cover over all the layoffs they were already gearing up for before it hit.
The tech industry is fucked on a colossal scale, because the whole thing has been a scam for the last decade, and they are running out of suckers.