Then why isn't it?! Why is it that the "recommended" client for iOS looks like something from 2005?
That's like asking why this tractor trailer truck still uses the same old boring shipping containers from 40 years ago.
The reference port is the reference port. When FB did xmpp, Google could read their emoji, for instance. It was a brief window before they both diverged from the standard for enshittification, but in that window it all just worked.