A huge benefit of stackoverflow, perhaps the biggest benefit, is that it is a single place you can go to ask about a wide variety of languages, frameworks, libraries, etc. and interactions between them.
Having to join a separate mailing list, forum, or chat server for every "community" you might have technical questions about, then keeping track of those is incredibly inconvenient. And in some cases it may not be clear which one to ask a question on.
That's not to say that such places for community discussion isn't valuable, but stackoverflow serves a different purpose.
Should have a desktop tool that allows you to subsribe to different communities and interact with them in a more coherent manner. That way people could self host, and as long as the site talks a common protocol, various tools can interact with it.
Then the site itself should have http output for the discoverability.
Having to join a separate mailing list, forum, or chat server for every "community" you might have technical questions about, then keeping track of those is incredibly inconvenient. And in some cases it may not be clear which one to ask a question on.
That's not to say that such places for community discussion isn't valuable, but stackoverflow serves a different purpose.