Honestly, I've noticed an uptick in the number of discourse forums for tech related things and I'm all for that. Discourse is documented well and maintained openly, it's indexable by search engines and you can visit and use discourse-based web forums using browsers that aren't capable of js rendering (think lynx). The last bit is a nice-to-have for me, but just being indexable is huge.
In 10 years, I would hate it if every answer I gave or got from a developer is lost to an endless abyss of messages buried deep in an obscure discord guild that a user would have to sift through only after making an account with and installing specific chat software. I hate there being so many hurdles in front of just getting answers. That's a good tl;dr as to why discord is on my shitlist for support/development discussion platforms.
Yeah see that's the sort of conclusive mindset that's got us here. I don't mean to insinuate you're wrong for coming to that conclusion, but "It costs money or effort so let's use a worse option because it's convenient" is part of the reason we don't have a lot of good solutions in this domain.
I'll also admit the options these days are limited depending on your goals for a project. If you want to reach the most eyes and have the highest draw of potential contributors, having a discord server makes sense. My gripe is when technical discussion or support take place there.