This must be the disconnect. As an Android user, it wouldn't occur to me that the "default" messaging app (usually something barebones and ugly) would influence

This must be the disconnect. As an Android user, it wouldn't occur to me that the "default" messaging app (usually something barebones and ugly) would influence how I send my messages. I just use whatever app I want, SMS or not. But unlike Android, Apple managed to popularize its own all-in-one messaging solution and in so doing brought encryption to more conversations. Google could try to do something like that with Android, but thus far they've simply remained agnostic.