If you block them (mozilla fb container is great for this) how do they connect your phone number in your friends phone when the facebook app scrapes it to your internet browsing on a third party site? Where I might live what school I went to and where I work seems like its public information already, maybe in voter registration databases.
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.
