There was a point where I
did try to use Signal in anger. It petered out almost immediately because nobody I talk to uses it except to turn on disappearing messages, shit-talk somebody else, and then go back to Slack or Discord. Because it does do disappearing messages well! But nobody I know wants to deal with it past that because contrary to your "it's just like everything else", its affordances are at best
not distinguishing and certainly not
good.
At some point, perhaps it will enter your consideration that talking about things like "people respect[ing] themselves and their data enough" is alienating to anybody who has a job and a mortgage and things they care about more than your minority choice of a messaging platform. Normal people don't care because normal people don't have governments, etc. in their threat models because normal people are boring. If you want to interest normal people, you have to be better than the BATNA--better than non-use. And saying "privacy" or "just get your friends to use it too" is a fail state.
Linux-on-the-desktop failed, too, when the only tool in the box was hectoring. (He said, from a Linux desktop.)