I don’t think the demise of classic forums/self-hosted communities is a technical problem. There is no shortage of modern communities - as you say, Discourse is one of the most popular. Otherwise there’s NodeBB, Flarum, etc - and vBulletin, IPB, phpbb, etc are still under active development.
The larger “problem” is the world has moved on. For its flaws, people seem to enjoy the familiarity/community of umbrella sites like Reddit.
The larger “problem” is the world has moved on. For its flaws, people seem to enjoy the familiarity/community of umbrella sites like Reddit.