The older folks make facebook sticky for the younger people too. It might not be their first choice for social media, but they're on there cause extended family are on there.
Some people quit facebook, most people don't. There's lots of groups, and now you have market place. It's genuinely useful.
Yeah my wife and I (millennials) have both been "Facebook is for Boomers" people in the past, but when I was into competitive card games all the events were organized on Facebook, and now that we have a baby there are all kinds of new parent groups that we use.
We still don't really think much of it as a social network but somehow while we weren't looking it pretty much ate Craigslist, Meetup, and Local News so now we're on the platform again. Like if someone has some baby formula they don't need, we find out on Facebook. If somebody gets stabbed at the pizzeria across the street, we find out on Facebook. If there's a card game tournament, I (found) out on Facebook.