Do you think 99% of the grannies and non-techies care? I support Signal and use it myself to communicate (with the 2-3 other people that use it…), but it’s not comparable with WhatsApp or Telegram which everyone has. It’s shitty but it’s reality. People even use Facebook Messenger over Signal.
Threema at 6€ is not really a good option for anyone anymore, a least not over Signal. Also they had an encryption obfuscation problem recently, read the longer comments at the bottom here and decide for yourself:
I know people who prefer Threema simply because they know what their revenue model is. Everyday I find that another person in my contacts has joined Signal. I don't communicate with too many grannies besides my own two, both of whom have Signal installed on their phones ftr. My circle clearly isn't your circle.