This makes me think.
What happens when partial profiles are matched to the wrong person? Like, it's very likely these systems are going to match different people in the same household/network because... how can they even separate different people with different interests and a single person using many profiles?
I suspect all our "valuable user data" is tainted by default and its monetary value is an illusion. We do know that the systems are overzealous, and the algorithms driving those systems are far from perfect (and in case of ML models, high chances of it being non-deterministic, to boot).
A friend recently got some of those ISP copyright strikes because the fiancee of his sister got relocated to his house for a few days and decided to leech from the network to download some AAA videogames. Of course the strikes were to my friend's name, because they have no way to know some stranger did it instead.
I can easily see my data profile saying I'm into horoscopes and that voodoo because my mother browses that stuff all day from the network assigned to my name. I'm sure there are attempts to defeat incognito/private tabs by bundling all "indecisive" data to the main profile in a given IP, so a large household can be a completely schizophrenic data profile with data mixed from a lot of users in that household. Imagine someone in your house has been using some extremist or taboo site. If that data is mixed up with yours, and a person with bad intent wants to take advantage of leaked data they obtained on you...they have a pretty strong weapon to assassinate your image. "You can't deny it, it's in the data. Your cousin did it? Oh what an ignoble attempt to save your butt, how lowly!". Since you have no way to plausibly deny it, it can be a strong blackmail weapon. Maybe stronger than medical data leaks in this weirdly political climate we got now.