I don't know why. I use the Discord server and don't like it, my messages get lost in the scrollspam and it's just a bad experience. Surely, a text field on the site would have been equally good.
you don't get to see other's images and talk with them in a shared chat channel with that approach (unless they build out a lot more web app). Which is half the fun of it. (Not that hard to build, but more work than a Discord bot.)
I like FPSes but I don't like multiplayer games. So I play single player FPSes, even if they are worse, because multiplayer ones are not fun for me. Craiyon, DALLE 2, and Disco Diffusion all offer a less social and direct interface in the same space as MidJourney and may be better to experiment with until MJ provides some sort of Web interface, as I imagine they will at some point.