Many of those things couldn’t be part of the standard. Modern encryption hadn’t been invented yet (and exporting it across borders was illegal) and many concepts simply weren’t a thing way back in the day. The extensibility of the protocol is what has kept it relevant for so long.
That said, the Modern XMPP project is trying to fix the compatibility issues caused by with the Swiss cheese of extension implementations.
Many of the things that XMPP listed as extensions really should have been part of the core protocol, in my opinion.
Many of those things couldn’t be part of the standard. Modern encryption hadn’t been invented yet (and exporting it across borders was illegal) and many concepts simply weren’t a thing way back in the day. The extensibility of the protocol is what has kept it relevant for so long. That said, the Modern XMPP project is trying to fix the compatibility issues caused by with the Swiss cheese of extension implementations.