Many people signed up after the new WhatsApp T&S debacle, but Facebook played it like a boss by delaying the change and draining the news cycle and they won.
Almost no body uses signal, I have chat group of my friends on signal, and I'm really thinking of moving it to WhatsApp, so they actually see the messages instead of it being 20 messages from me and 1 from the others.
Its not that they don't have signal installed, they just never open it, I use it as a video/voice call app and it works well, but messages? Its a PITA to get people to actually read them, especially since many of them are complaining of notifications not working.
I like the stories feature, especially because its totally encrypted, but its basically useless as almost no one in my social circle uses Signal.