That may be true for privacy advocates, but many people are not used to different apps for what they see as the same thing (texting).

They don't get why they have to use a different app to talk to me when this other one works fine for everyone else. "Why can't I just enter Dr. Hax's phone number and send him a text with the texting app that I use for everyone else?", they wonder.

So, to them, it's more confusing to have different apps. They don't see any difference between Signal and Messaging. And that was the beauty of the old Signal: they didn't have to know about these underlying security features.