The fundamental question is: why should I use Jabber? What's the use case that makes it better than WhatsApp, Signal, et cetera?

My most-used messaging app is SMS because if you have a cell phone, you have SMS. Example this morning is I made a connection with a handyman recommended by a friend. Text message, and it just worked.

So what's the compelling reason to move to Jabber? Why should my 92-year-old mother use it?