Are you in the US? I get the impression that iMessage and RCS are only big there. Almost nobody uses them here in Europe. (It's mostly WhatsApp where I live and Signal is slowly getting more popular.)
As an aside, from the latest release notes: Sandboxed Google Play compatibility layer: add toggle for granting Play services access to ICC auth in order to support RCS with carriers requiring it for RCS in Google Messages including T-Mobile (see RCS usage guide)