The idea of making Apple use it is also part of Google giving the operations to carriers, just like SMS, and then gradually replacing SMS altogether. Google isn't even supposed to be running the RCS servers. But they did it in order to get the standard up and running everywhere. It's an open standard, and multiple carriers in several countries are on their way to carrying the burden of the servers, the way the standard is supposed to operate. Once it's operating, all servers can talk to each other, just like you can SMS a person on another carrier line. RCS will allow universal rich texting.

Surely XMPP and other standards are different and I would prefer any other than something championed by Google. But the truth is, that the other standards aren't invited to sit at the right tables and don't offer the same “replace SMS once and for all” potential the way RCS does. XMPP for example is super expensive to escalate and like almost all of the traffic is just presence messaging, which is super wasteful and energy intensive on servers. RCS is not the best, but it's one that all carriers and telecommunications agencies are on board for replacing the archaic SMS. And it doesn't preclude using other protocols. Like, WhatsApp, Signal, Matrix and Telegram will still continue to exist.

I'm not so sure about the special license thing. The limit on 3rd party apps is because there isn't an API in Android that exposes RCS to users, only OEMs (which is how Samsung can do it). If Google flipped that switch and made the API public, 3rd party apps would be able to use it just as easily as they do SMS without paying extra or obtaining a license. It's an open standard.

Only Google knows why they haven't done this already.

Also, encryption is a mixed bag depending upon the client, and you need a phone number. Using iMessage with an email address is quite nice.