If the relationship is valuable to you, it requires maintaining. Following each other on social media isn't the same.
Not to mention social media is filled with someone's best moments which give you a bad view on how you're doing against your peers.
Not to that half of the posts on social media are ads, which aren't good for you at any age.
Maybe not to you, but to some people it is incredibly valuable for maintaining relationships. And these are kids about to part with most of their friends for the first time, you can't rely on them having learned your insightful life lessons by this point. I'm guessing you've never been felt the negative effects being left out of a social circle can have? Relationships aren't binary, not everyone is best friends or strangers. Lots of room in between for people to bond or be left out.
I grew up in a pre internet world. We had "negative effects being left out of a social circles" then too. Social circles being hard is not going away regardless of how this decision lands.
The fact that you never grew up in the social media world highlights exactly why you don't understand the problem despite thinking you do. Your good old "social circles being hard" issue is not the problem here.
Please understand that there are plenty of situations where someone gets invited to something if and only they are visible to others and easy to invite. i.e. there exist plenty of situations where being on the platform is the sole determining factor. And that being off the platform that the majority use puts a very significant, ongoing, and asymmetric burden on the host (or invitor, if it's a different person) to keep them posted on all the details that did not exist otherwise, and this fundamentally makes one less likely to be included, in an entirely natural and unavoidable fashion that is no fault of anyone involved, and has nothing to do with "social circles being hard".
You have to recognize when the system is making a problem worse than it naturally is.
The irony. How can you be certain that it's not social media making "problem worse than it naturally is"? Many people believe that social media is.
As someone who was not particularly visible, and was not invited to every party, I am very aware that "there are plenty of situations where someone gets invited to something if and only they are visible to others and easy to invite". Is "not being on social media" really all that different than "not being on the <insert sport> team"? The same arguments apply. Easier to see and invite teammates, more social cache, etc.
In any case, if all teens were off social media then it would not be a determining factor, and I'm sure alternative systems would emerge for inviting people to places.
Communication is incredibly valuable for maintaining relationships. Whether that's through social media, IM, calling them, hanging out in meatspace. THAT is valuable. Not merely following someone on social media.
I am in my early 20s. My highschool life (and some after) was filled with social media use and borderline addiction. I added people on social media that I kind of knew, or talked to once, or wanted to talk to.
But literally none of that kept me in touch with most if not all of them. More than half of them I never messaged, never interacted with on social media.
What kept me in touch with them was me or them. I deleted all my social media. And the ones who make the effort to contact me out of social media? Those are the real relationships.