They bought an implementation of RCS, the standard is still open. They even sell there implementation to a few telcos.

You cant self host it because you need to be a telco, it has telco specific protocols. Also, this is one of the things that probably should be gatekept to telcos, if everyone were able to spin up their own instance, the spam problem would be unmanageable.

Your looking for a conspiracy/monopoly that for once, doesnt exist due to Google being malicious. It exists because telcos are shit.