Re: Why do they track you?
You can still apply the same model: target the ads to the *content* that people are consuming on the site where you're showing the ad.
It's a model that probably even works better anyway. I've always suspected Google et al. just claimed at the time that their "behavioural" tracking was better, just to differentiate themselves from the competition.
I don't have any evidence about Google et al. themselves, but that is what those guys from Oxford Analytica claimed when they were selling their political campaigns, and it is known that it didn't work at all.