Google famously campaigned for Apple to "get the message" and use RCS, but now doesn't let rooted Android users use RCS.
TL;DR
Users who have rooted their phone, have their bootloader unlocked or are using some custom ROMs report that their RCS messages are not being sent, even though RCS shows them as connected.
The Google Messages app does not show any error messages when blocking RCS messages of these users and does not send the messages out as SMS or MMS either.
Google famously campaigned for Apple to include RCS messaging in iMessage but is now blocking it for certain Android users.
The thing is, RCS isn't SMS. That's kind of the point. RCS is a replacement for SMS. The two protocols just happen to be available in the same Messages app. It's like sticking WhatsApp inside Messages, except it's a different protocol.
That is what blew my mind indeed, and as someone who hates constantly dialing companies and such for minor crap, I kinda am glad they went this way lol.