The old saying is that if you're not paying for the product, you are the product[0]. The argument is usually that when you're getting things for free, you're being sold to advertisers in some sense. But it could just as well be that if you're getting things for free, the ability to influence you is being sold to those who want to influence you. In fact, with sufficient cynicism, all sorts of such theories can be considered plausible. Your experience seems to indicate that perhaps one does not need that much cynicism.

0: I've never thought much of the saying because I think you can have multiple people participate in an economic interaction.