There has been some weird misunderstanding on the business models of ads network. They have zero incentive to sell user data to advertisers or whoever else. That data and model is the only meaningful difference between ad networks, advertisers and their potential competitors, beside of established infrastructures. You don't sell your strategic weapons to your enemy right? They may provides some targeting and contextual information for bidding, but given that many ad networks are moving to automated bidding systems I think this also will be gone eventually.