The problem is that the only one XEP that could allow for a Discord-like UX (XEP-0503: Server-Side Spaces) that, let's admit, is the best one for many (I, in example, prefer that UX over the IRC or plain contacts + MUCs list UX [like, the WhatsApp, Signal, Telegram or most XMPP clients), is only actually used in one client (Movim), and only other one has discussed implementing it (Gajim, that has something like a Client-Side Spaces impl that is really prone to break up), has only done that, discuss it.

And why it's a Discord-like UX better, in my opinion?

Because it allows for more structured, focused and topic-based conversation and discussion. That's why that UX has gotten so popular among not only gamers, but also among students, freelancers, creative groups, or even scientists and companies. It's less prone to become a mess than a plain list where everything is mixed up.