I was wondering about that the other day. Why did Jabber/xmpp not evolve further into the mainstream? For a while there were multiple good-enough clients and running ejabberd was not very difficult. I thought it would become ubiquitous (and in a way it has, just not interoperable), and the clients would evolve to become great. Instead it feels like the whole ecosystem kinda just faded away.
I remember why we switched away from Jabber (running ejabberd) in our company: the biggest issue was no server-side history, so using multiple clients on multiple devices was basically impossible, just like MUCs without history to browse and search were useless for our use cases. Has that gotten better over the last 10 years?
We switched to self-hosted Rocketchat, so which sucks in many, many ways but feature-wise it offers everything we were missing from xmpp.