From what I see, it's less important with young adults now than it was a few years ago, and it started as something only for young adults that spread upwards through the age groups. It could be reaching a stable point though, true.
The whole "facebook isnt cool anymore" thing has been going on for a decade now. Linkedin isnt cool. The WhitePages arent cool. Plenty of other properties, like twitch, discord, twitter, carve out their niche. Snapchat was going to be the facebook killer, people got bored with snapchat. But facebook keeps growing. Now TikTok is looking like a threat. But no matter what everybodys favorite place to hangout is, they also have a facebook. And companies keep throwing money into facebook ads.
