Granted, it has been a couple years and it could be a bit better, but XMPP is a horrible, horrible protocol to work with. From the ground up.

Matrix might be bloated nowadays, but that's nothing to the horribleness of xmpp.

source: I wrote the first xmpp/matrix bridge in 2015

It's not the reason, but it certainly is a reason.

Another reason is. That it is an old protocol from the late 90s. And there isn't a lot of Buzz about it these days. A lot of the problematic centralization we all now recognize was just becoming the norm.

Feature parity at the time is also another big hurdle. Things we all take for granted especially in this day and age Avatar profile pictures etc. Jabber/xmpp did not have that for years. It may be a useless feature in terms of sending messages. people still like personalization etc. And it's hard to convince people to switch if they have to give it up.

Jump to today. And arguably services like Twitter Mastodon Facebook Etc all sort of fill that Niche to an extent. Maybe not as well. But enough again that it's going to be hard to get people to switch to yet another system

I don't usually hear this opinion.

Most of the time, it's about how XMPP has everything you need without the boat of a Matrix server.

Eh, only if you squint reaaaaally hard

In practice, you will run in constant compatibility problems. Let alone barely functional multi device support

xmpp is closer to IRC than to modern communications protocols. End-to-end encryption, for example, is an optional protocol extension, which hasn't even been formally finalized yet (and probably won't ever be, given it's been 10 years now)

I've run an XMPP server for a small online user group for about 7 years. It was relatively simple to get a basic server up and running.

One challenge came when my wife and I decided to use it as our everyday mobile messaging service. I had to learn about and configure a number of extensions to get Prosody working well with Conversations (Android) and Monal (iOS).

Another challenge was filtering spam. I posted my administrator XMPP address online and got hammered with spam. It took a while to figure out how to effectively combat it.

With respect to why it's not more popular, imagine if you were trying to sell people on email (with no business use-case). It's a generic federated protocol. I don't know if you can get much more bland.

I never really did very much with IRC on a protocol level. I just know that it's ultra simple, and suffers similar problems as xmpp: it's not really meant for multidevices with a shared backlog.

I'm sure there are projects to enhance IRC with proper e2e encryption and chat sync, but you really want something that has modern usage in mind from the ground up. IRC and xmpp are just very 90s.

note: it's now been a couple years since I last took a deeper dive into xmpp and matrix, so things might have changed. But especially for xmpp, I can't really see how without breaking compatibility. The protocol is just very... special in its own way

Conversely, I have seen this opinion expressed a few times. I can’t judge the accuracy but there seem to be more than a few people sharing it.