facebook was for college age people. facebook is still for adults. when kids grow up, and go to college, if they dont have facebook, they get it. just because kids are allowed to join, doesnt mean its designed to appeal to them. its purpose is to connect people. friends who see each other every day dont need many of facebooks features.
this "kids dont think facebook is cool" narrative has been going on for years, and it just doesnt matter. they come around eventually. the network effect is too strong.