Why is the public only concerned with Facebook selling data and not ISPs selling data?
This will be controversial but I think the reason why Facebook suddenly got to front-pages is an alleged use of its data for Trump’s campaign (and other political purposes). I’ve been a post-doc at Cambridge Uni in 2007–08 and I remember a lot of activity around Facebook as its data was easy to collect (in that instance the research was about social networks, trust, … one particular research area was to produce models of social connectivity for simulation of security threat models in large networks). There has been loads of research papers using its data and no-one was bothered then nor anytime up to 2017.
Also, I think that ISPs probably did the “expectation management” a bit better and have been quite open where they stand in terms of the “personal data and free speech” context.
(One thing I’m still not quite sure about is whether the data sold by Facebook would be subject of e.g., the new European GDPR regulation protecting personal data. The thing is that the data in question is unlikely to identify particular users - their names, email addresses, real addresses, and so on. )