I wouldn't say XMPP did not change for 20 years, have you seen https://conversations.im/ ? Except voice / video (that I personally use rarely either way) I don't see any important modern feature missing.
Not saying it didn't change, that remark came from a non tech friend of mine, and it's hard for me to disagree without getting into boring technical stuff they're not interested in.
I'm not talking about boring technical info but user visible changes like easy image / file sharing, "X has read until this point..." etc. They are small changes and already present in proprietary solutions but for users this is a visible change.
I put my entire family on a self hosted server and for them it looks like any other modern messenger. (no voice video calls yep).