Different applications also supported different feature sets. Keeping up with ever newer supersets also stretched many players’ resources too much: https://alexalejandre.com/programming/xmpp-open-messaging-st...

> A more rigid core standard, actively keeping up with new technology may have delivered XMPP’s federated dream. In reality, each sever supported a different feature set, while lacking common features every other chat app offered. As mobile technology transformed, XMPP stayed still. Pidgin worked on Google Talk, before an XEP brought (necessary) OIDC authentification and those 3rd-party clients couldn’t keep up.