I see the matrix is more popular than xmpp, but why?
more popular
That’s not true at all. There are a ton of business applications for XMPP from IoT messaging, to Nintendo’s user presence, to being a 90% chance your favorite online game’s chat back-end. Behind Jitsi & Zoom & WhatsApp is an XMPP server. Matrix by design will never scale to these demands if history needs to live forever & all servers need to duplicate data.
More trendy would be a more appropriate phrase since Matrix wants to chase after proprietary Slack & Discord, where as XMPP is extensible & more generalized for all sorts of applications. Even with all of these proprietary applications, there are plenty of open communities hosted for MUCs & also blog/community thru Movim/Libervia & as an alternative back-end for UnifiedPush, etc. With the server resource usage being much lower, it’s cheaper & easier to maintain an XMPP server alongside another application in a VPS or even on a home network with dynamic DNS. If you are inclined, set one up & test it out.
I have never used matrix but why would anyone design something that won’t scale by design?
I understand scalability not being a priority but designing something to be poorly scalable by design seems odd.
If you want the messaging to be resilient, this makes sense as a server can go down but anyone else connected has the whole history on their server.
But I think that is better suited for a forum where copying Slack/Discord’s lead & trying to preserve all history in a chat isn’t worth it as I see this sort of thing as better tasked for ephemeral communication. However, there is something communal & intuitive about chat apps that make folks interact pretty well so they can make decisions. This is a ‘good thing’ where forums don’t get the same engagement—but at the cost of you had to be there or worse, you need an account to see the discussion for that decision.