And gave a constant reminder to people that something better was right there.
And put things in one place.
You're letting perfect be the enemy of good. At least with SMS support I could get people to switch to "this new texting app", and we'd then have a proper Signal encrypted chat. And when they texted someone else, Signal would append the "you could have encryption too" signature, generating a conversation about it.
The people who moved off of Signal went back to SMS entirely. How is that better?