YSK: Signal is a great secure private messenger app comparable to others on the market.
I was so bummed when they removed that feature. I didn't really understand why viewing SMS in the app was "not secure enough".
Inside Matrix, the protocol that might finally make messaging apps interoperable
Google. XMPP was getting a lot of traction so Google started to support it in it's chat clients but then after they got people on Google products they slowly stopped making all features XMPP compatible. This caused non Google XMPP clients to have a sub part experience. This pushed people to switch to Google or lose the ability to talk to friends using Google.
This is a tactic referred to by "Embrace, extend, and extinguish"