Comment by nostrademons

They don't, at least not necessarily. I look at my HN history and it's 13 hours ago, 6 days ago, 8 days ago, 13 days ago. Fifteen years ago I was #2 on the leaderboard (itself now gone, it listed users by total comment karma) and would post about 4-5 times a day. Now when I'm not posting, I'm actually not on the site and not reading replies. I just don't have time.

I think a decent-sized subset of Millennials have basically aged out of the time-surplus years of the early 20s and are now busy with kids and careers and families. And they aren't being replaced by the new 20-somethings, at least not on social media of the same form. The kids are still on text messages and Whatsapp and Discord and Roblox and Google Docs (!!), but they aren't interested in getting on the public Internet, and if they are, their parents won't let them.