Google didn’t buy it, it’s an open standard.

What google did is host RCS infrastructure and have the worlds most popular messaging client.

You can absolutely setup an RCS server, build an FCS client that has the appropriate keys and access, put RCS relays in important peering points a over the world, and roll that out to millions of ppl yourself.

Sort of like nuclear power; you could probably build a reactor yourself, but it’s a heavy lift plus there are players that don’t want you to.