You are more correct than they are but are still wrong*. A lot of the interest in XMPP died after they started pursuing standardization and of course after Google close off their servers. It never had a ground swell before or after that either though. XMPP however, still exists to this day. And has become integrated into internet of things, protocols for communications between devices and as well as more comprehensive communication services such as SIP. They literally just had their 2023 Google summer of code complete a month or so ago?

But yeah XMPP is not dead. Unfortunately, it was a surpassed by a number of other services that offered more. Evolving faster than XMPP could while looking to become standardized. It only lost relevance to most. Not it's life. For what it's worth since 2000 or 2001, there's hardly been a day that I have not been logged in to an XMPP server. I'm logged into one right now.