I still don't understand why Matrix was made when XMPP is already a thing; if you're not happy with the existing standard participate in the process, don't just make up a new one. https://xkcd.com/927/
XMPP instead is federated messaging and presence (and a whole bunch of stuff on top). It's passing stanzas between servers rather than synchronising historical stanzas between servers. The specs are highly modular and extensible and built out of XEPs. It's just a totally different way of approaching the problem of open communications.
You could make the comparison that XMPP is a bit like SMTP, and Matrix is a bit like NNTP (Usenet). They both fulfil the same end goal - letting folks communicate openly over the internet. But they have totally different designs and there's room on the 'net for both.
After all, you can just bridge XMPP to Matrix and everyone wins! :)
There's a larger narrative, I think, about how standardization bodies that are focused on backwards-compatibility can move more slowly than a newly-built ecosystem. While the web has huge commercial players dedicated to making it a first-class experience in an interoperable way, it's unclear that XMPP has the same impetus to evolve. Google Wave could have saved XMPP, but look how that turned out. I think it's very reasonable for Matrix to unfetter themselves from XMPP politics in a world where Slack the Quadricorn is the gold standard.
Have you tried... thinking about it a bit more? I could come up with roughly 20 different reasons without trying very hard. For someone involved in XMPP, that is one hell of a thing to say.
Seriously, calling out XKCD927 on a massive project like Matrix is extremely disrespectful to its contributors.
Tell me, what could Matrix have done to save XMPP? Publish a hundred different XEPs nobody would ever bother to implement? Make broken clients/servers that don't follow the spec just to try fix a protocol that lost? Magically fix everything and tell people "No really guys, XMPP is better now I swear!"?
They went and tried a new approach and they're doing really well with it... have some respect for that.
For me, the more I learn about Matrix, the more persuaded I am that it really does have merit. If I were a Matrix developer, I wouldn't feel disrespected. I'd be super glad that people are asking questions and genuinely seeking to test that the idea is right. From their dialogue with the community that I've seen so far, the developers are doing great and seem to thoroughly appreciate there's been a lot of false starts by various groups over the years.
TLDR;) - It may be obvious to you, but it's GOOD people are having the conversation. Questions and even dissent should be embraced. It's not about disrespect, it's about testing & validating new ideas.