With an app it is just me, the app and whatever internet connection I have.
With SMS&co instead I have to deal with a system outside that, managed by the phone company and whatever.
Also apps are constantly updated, RCS standard will just become SMS2.
Even iPhone users use an app in USA, it is only USA android users that for some random reasons are still stuck to SMS.
Here I just open telegram or whatsapp and message with anyone, no matter the phone. Or discord, or Matrix...