Actually I've been seeing a big uptick lately. A year ago it sat idle for me because no one I knew used it. Now it's about a third of my conversations, maybe more. I'm quite happy about that. The competing platforms for "message people in a sensible way across platforms" are basically Google chat (whatever they're calling it this week), and Facebook messenger, and I feel much more comfortable with signal over those two. Oh, there's Discord too, but not many people use that as their regular one-on-one messenger.