That plus the handful of people I personally know that are various forms of activist or just interesting, with whom I wouldn't stay in touch the same way if they were on blogs, email newsletters or IM groups.
What fb got right apart from capturing the network effect at the right time and place was that it struck a balance between blog, microblog and forum that neither MySpace, Twitter, Discourse nor even Friendica/Hubzilla/Streams have. Google+ came very close before they suddenly gave up. Diaspora might be the closest thing still running.
I don't even know exactly what it is. Maybe it's actually just G+/Friendica/Diaspora but with more people and with my uni acquaintances.