Well, that´s all what "google" and facebook are about: personalized commercials and advertising. They try to give you those kind of "temptations" that you most likely will "bite" on. Maybe cleaning your cookies and going to a bunch of car sites (Audi, BMW, Toyota, GM) will solve the problem and you´ll get mostly car advertisements afterwards.
Zwei Dinge sind unendlich, die Dummheit und das All...