I'm not even talking about the free services, though.

I am talking about the ordinary consumer goods manufacturers that buy the ad space that may or may not be sold on free online services. They're the ones who want that ad space, who benefit from the targeting, and who make the whole operation work.

The "how" they make money and how they secure, anonymize and to whom they share it are all important considerations that are almost exclusively(there are exceptions) never divulged.