1. They probably still track your 3rd party app usage, which is not as easy to block as on the web. 2. Since they have detailed information about your friends

1. They probably still track your 3rd party app usage, which is not as easy to block as on the web. 2. Since they have detailed information about your friends the contact graph has enough information to predict your age, probably what your major was, political leanings, etc. Not to mention photos of you that might have been posted by your friends on facebook. 3. They used to buy 3rd party data that they could join on your phone and email address. Sure some HN users might have enough knowhow to block most of their tracking but 99% of facebook users don't.