My participation in Facebook has fallen pretty sharply as well. While I have a modest number of friends on Facebook, I do not post there any more, and only visit when I get e-mail notification that one of my friends has posted something of possible interest, to which I may or may not make a comment (usually something quite pithy).
And I have NEVER joined Twitter, as I do not even have a phone with texting capability. At my age, I do not want a phone smarter than I am. And who can handle those little bitty keyboards, anyway?
I’m with you,alloy. To text on my little keyboard I bought a small stylus that plugs into the headphone port. I don’t use it much but have it when I need it.