And what does it mean that I’ve never even heard of either of these?
Exactly.
Facebook never interoperated with any of those, or any other platforms, so I’m not sure what your point is.
Facebook messenger literally integrated with XMPP to do exactly what Meta is clearly planning with Threads. They added compatibility in 2010, then scrubbed it in 2015. It's right out of their own playbook. Your assertion is factually incorrect.