As I have said repeatedly, Facebook was great until people got bummed out that their fake exciting life and airbrushed selfies were not as great or received as many likes as other people's fake exciting live and airbrushed selfies.
And now people are self-reporting to Pew they are not using it as much.
Facebook isn't cool anymore, and always had a "Wal-Mart" feel to it. It great when mommy and daddy didn't discover it, and couldn't sign up. Once the luddites started going on Facebook, it wasn't fun anymore.
Facebook was the cool kid who hung out with you until you discovered they were just using you, and you weren't getting "discovered" by the other cool kids. It lost its lustre. It got sent to the principal's office a lot this year. Your relatives weren't converting to your politics no matter how many meme posters you plastered up on your wall. It wasn't fun when people de-friended you, and you had fewer friends than your sibling whom you were always insanely jealous of.
People under thirty were made to feel depressed because of the competitive rigs of Facebook, and if you can't dominate, you tune out. It was never raw, real, or brutally honest.
It is amateur self-promotion, and when it fails to deliver after a decade, people do eventually clue in.
And to be exploited in your misery by the cool kid changes your perceptions of what cool really is.
Memo to the Internet: cool isn't corporate. It is not Establishment.
And it isn't 2018...