The tiny company behind Signal, and a bunch of even smaller companies making messengers, manage to make their app work just fine on iOS and android (and most of them on desktop too, some even in the browser).

For some reason, the (second) richest company on the planet, which has a messenger app, is incapable of making an android app for their messenger and chat protocol.

There's a technological issue, and it's nothing to do with RCS or SMS, it's that iMessage for some reason doesn't have an android version.

To be clear, I'm not saying it's a technological limitation Apple can't solve. Apple originally intended to release iMessage as a cross-platform protocol.

The technological problem isn't whether Apple could fix it, it's the fact that they haven't. So, group chats with one green bubble just work differently than group chats with all blue bubbles.

It's a business decisions to do vendor lock in. "Free market"