How do you sell highly targeted ads without revealing your data? How did the Obama campaign download the entire U.S. social graph in 2012, and brag about doing so, with Facebook’s approval? How did Cambridge Analytica do a comparable thing in 2016?
They abstract most of it away. Marketers can set specific targeting criteria and can get a high level estimate of how an ad will perform. Beyond that it's tracking impressions, clicks, split testing, etc.
The app API was different until 2013(?). App developers only needed a single user's permission to access all of that user's friends' information. Both Obama and Cambridge Analytica came out of that period. Now, users can only authorize the release of their own information.
Facebook doesn’t sound that jealous to me.