I still remember writing an XMPP-Client and IRC-Client servers which were widely used across our organization. Later on, we developed our cloud-based chat application with mobile apps. Then we had support for xmpp/irc for those chat apps, eventually dropped the xmpp/irc support too. I think the reason is major players (Google/FB) dropping the support for xmpp and at the same time evolution of many cloud-based chat apps.
XMPP is well standardized and documented. If it could have been TEXT based instead of XML many developers could have adapted (IMAP protocol still being widely adopted).