The apps being able to siphon 10s of millions of user's data makes what you're saying you can't do possible though: you use an app to get everyone's data, then

The apps being able to siphon 10s of millions of user's data makes what you're saying you can't do possible though: you use an app to get everyone's data, then you analyse that and work out the groups you want to target and with what. Then you realise that the best way to deliver those ads, given your data is Facebook profiles and all your targeting categories are from Facebook, is with Facebook ads.