What they provide to marketers is access to the platforms. They'll say to the marketers, “We won't give this to you, but you tell us what kind of people you want to hit, for example, members of the ethics committee, and we'll do our best to direct your ads to those people.”
A similar thing is, if you are the marketer, obviously, you won't have that information. You will indicate your target group and say that you're looking for certain characteristics. Then a social media platform will do its best to display it to those people. Certainly, the advertisers don't have access to that.