During your teenage years there’s a lot more FOMO as you are trying to establish yourself in your peer group and the social hierarchy in general. This must-check-that-notification then compelled them to react to it, which generates more notifications in a feedback loop.
Compare that to now, when I’m in my mid 30s, if an app generates too many notifications I will revoke its permissions to notify me very quickly, all of my social interactions are more asynchronous and slower and deeper, since I’m not being interrupted by notifications all the time and am communicating on my own terms