I think that with the rise of push notifications, no one really goes to a site to check notifications anymore. So the new user may have not developed the muscle memory to go back to SO and participate. I suspect this also has something to do with the decline of forums. Reddit still works because the app sends 200 notifications a day, but without it, I don’t think it would be as popular.

Also SO is participation hostile unless you’re a pro, so as a newbie I’m not going to do anything other than ask and lurk, because I’m not worthy