And Instagram + Snapchat are more about looking at what your friends are up to, and offer way more intimate experiences than Facebook. I have never seen a link to a news website or political ad on either platform, but Facebook is littered with them, and it crowds out the content I want to see: pictures of my friends doing cool stuff. If I want astroturfing and news, I go to reddit and HN :P
So Facebook occupies the awkward middle ground, and most people I know use it to collect acquaintances and to exchange Instagram/Snapchat handles.
Source: am teen