It's too late to add an edit comment, but I'll agree with all of the replies - this was a gross overgeneralization of how these companies structure their advert

It's too late to add an edit comment, but I'll agree with all of the replies - this was a gross overgeneralization of how these companies structure their advertising programs. They _use_ your detailed browsing history and social interactions sell other services to advertising companies. Their internal properties (at least Google's) have direct access to this data to aid in their own advertising programs (not 3P, but maybe not what you expect). I didn't explicitly say they give that data to 3rd-parties, but I'll clarify that they do not give the unanonymized data to third parties (analytics from campaigns provide a fair amount of anonymized data). To the best of my knowledge, there is no method of getting discrete, individual specific data directly from these companies unless you have a subpoena.