XMPP had rather bad name. Well-known design issues causing message losses, fractioned ecosystem due to varying implementation of extensions, unsuitability for mobile clients, absence of synchronization between clients, absence of end-to-end encryption. Most of these issues were (much) later fixed by extensions, but Matrix (or Signal for those who do not require federated one) was already there, offering E2EE by default.

Even today, E2EE in XMPP is rather inconvenient compared to Matrix due to absence of chain-of-trust in key management.

> I am genuinely interested in hearing why we collectively ditched XMPP

We didn't. It was never very popular, and is today more popular that it has ever been.

Google Talk support for XMPP: 2005-2013

Facebook Messenger support for XMPP: 2010-2015

Jabber.org support for new accounts: 1999-2013

First-class integration with two of the world's largest social networks put XMPP in practically everyone's hands for a time, but when all the major hosts left, network discoverability and typical account longevity dropped drastically. The landscape is bleak today.

And since then, our collective needs and expectations of a chat platform have expanded. XEPs have been developed to bolt much of that functionality onto the base protocol, but that has led to a fragmentation problem on top of the bleak server landscape.

This unfortunate situation might be navigable by a typical HN user, and perhaps we could guide a few friends and family members and promise to keep a server running for them, but I think the chances of most people succeeding with it are pretty slim today.

Decent overview (& more broadly but the heart is about XMPP & good ol’ capitalist corpo greed): https://ploum.net/2023-06-23-how-to-kill-decentralised-netwo...