Or maybe some people just want to keep their life as simple as possible, attention economy and all?
With my mid-30's I don't consider myself "that old", but just the idea of having to manage through a dozen different messenger apps is driving me super anxious just in the same way I like to have all my email accounts in one client/app and not spread across a dozen different clients/apps.
There's also something to be said about efficiency; Keeping up with a dozen apps (not just in content but also software version) is a whole lot more effort than doing it with just one app.
Maybe I'm actually that old? I just think simpler is usually better and to me, there's nothing "simple" about doing the same thing trough 12 different apps, to me that feels counter-intuitive and in the context of Internet communication, very archaic.