To put it another way, Google can't kill SMS short of literally removing the app from Android because it's not their infrastructure, but if they shut off their RCS servers tomorrow, it would be dead for good. That's a Google-only service.
They could just layer their own chat platform on top of Google Messages but we all saw how Google's IM business went along: Chat, Hangouts, Alo, Meet etc. So they muddied the water so deep (to a carrier level) to make it look like it's Apple's issue for not adopting RCS. And people actually fall for it.
Nobody wanted RCS. Even carriers don't want to maintain RCS. They just use Jibe. And that's exactly what Google wanted. My RCS communication with friends don't even show up in carrier's usage. How is that ever different from iMessage...
You know who chose to selfhost their own RCS server? Yes, Chinese carriers! They call it 5G Message. New ad delivery channel for businesses hooray! Instead of plain text and a link, now your campaigns can even have MENUs inside! I can send SMS to a Chinese number, I can send iMessage to a Chinese number, but I can't send RCS. Truly "Universal" profile.
It's a complete shitshow.