So true. It's hard to get my own family to even use Signal peer-to-peer with their other friends that are on Signal. They all default to the most convenient, plain text messages, even though it takes literally no extra effort to use Signal.
Discussion
I just told them. "I'm on Signal or Threema. Hope to see you there."
Thankfully, the most important ones came over (although they keep using WhatsApp etc. for other normie things). Others didn't, and I no longer communicate with them.
Try this, wait for a month, and test how many of them are interested enough to be in your life :)