Yeah, but a lot of that is because of adults going along with it.
I was about to say, in the past, adults didn't stop kids from having their fads, nicknames, etc, among themselves. Teens were goths, or punks, or metalheads, they had weird names, parents mainly ignored it and kept using the kids real names, kids expected this. So the adults represented something above these kinds of shallow attempts at identity creation, which the teens themselves eventually grew out of. Maybe they still loved the music, even the style, but they clearly understood it wasn't essentially to who they were as people, and that public life sometimes meant wearing a cheezy uniform rather than your preferred togs and you were still you.
However, I have suddenly thought - I have noticed, probably since my kids were young, an increasing tendency for parents to still themselves keep these identities somewhat, and especially to try and transfer them on to their kids when they buy them clothes, send them to activities, and so on. Lots more adults into things like comic cons, for example, and much more strongly invested than many teens were when I was young going to that stuff.
So maybe identarianism is just more of an extension of this. But in any case, I think adults need to show the way.