Network effects. As long as the other kids socialize on social media, not using social media becomes a drastic socialization penalty. The problem cannot be solved individually, only by collective action. Most parents must ban social media (and electronics in general) for their kids. Which indicates a need to pass laws to ban social media for minors. Bans and teens don't usually work as intended, we probably also need a wide campaign of stigmatization of said social media, akin to anti-smoking campaigns.

plus many schools etc are using facebook etc to disseminate news... and many kids friend prefers to communicate in facebook groups. Many teachers are also available in facebook.

In short: Network effect.