“Communication platforms like WhatsApp, Google Talk, and Zoom use or used XMPP under the hood, and others like Facebook and Microsoft allowed for XMPP intercompatibility.”
Big tech built its chat apps on an open protocol and then sold them as proprietary products. Facebook and Microsoft once let outside XMPP clients talk to their users. Neither does now. The protocol never failed. Open chat was bad for lock-in, so the companies walled it off.