4 pane comic of dolan on the left and spooderman on the right
pane 1 (dolan): cum join opensurce cummunity!
pane 2 (spooderman): shure! how joyn?
pane 3 (dolan): Here discord! (with discord logo)
pane 4 (spooderman with tears in eyes): y u do dis?
What is really happening is that people are looking for documentation or support, seeing that the forum, the IRC and the Matrix are dead, that the only other thing is discord, and give up. Minus some fraction who already use it for other purposes (gaming, probably) and don't mind using it.
But from your perspective, it looks like everybody is joining discord and liking it, because all of the other people just give up. It's only a very particular demographic that uses discord. Most likely (I might be wrong, but this is what I guess) very young, male, gamer, european descendent, and from a relatively wealthy western country. That's a very small part of humanity.
If you as the maintainer go and use the forums, and maybe announce this in discord, the users will follow.
Like a survivorship bias?
Ooh! I'm surprised that somebody made the same conclusion, but from a different perspective.
We have been using the forums. It's been announced in Discord, we have a webhook that posts in our main Discord channel every time there's a post in our main forum section. Every announcement goes to both the forums and the Discord, and the Discord announcements link to the forum posts.
We are using the forums. Our forums are still dead.