it’s sent over carrier networks and the carriers decide whose infrastructure to use.
The carriers never bothered to implement RCS; they just outsourced the whole thing to Google.
RCS is an open standard
That nobody uses.
it is the industry standard for SMS.
It's meant as a replacement for SMS. It's not just some new version of SMS that Apple hasn't upgraded to, which is what you were basically saying earlier.
It’s literally why every other non iphone can send high quality pictures to each other.
It's a messaging service used exclusively by Android phones. iPhones all support iMessage; Androids (mostly) all support RCS. All of those iMessages go over Apple's servers; all of those RCS messages go over Google's servers.
For what it's worth, iPhones have supported sending full-quality pictures to everyone over a legitimately open protocol since launch day. It's called email.
Apple not adopting it is anti competitive.
Google's attempts to legally force Apple to adopt its proprietary platform is transparently anticompetitive.