I happen to have a son who is currently is high school. While it is true that he (and likely his peers) is not a heavy user of FB, he does use it to coordinate

I happen to have a son who is currently is high school. While it is true that he (and likely his peers) is not a heavy user of FB, he does use it to coordinate events, and he does use Instagram and WhatsApp a lot. "FB" is not just "FB the site". If you listen to their earnings calls, a lot of time is devoted to Instagram in particular at the moment.