I'm not going to pay $6/month for each person who wants to sign up to check it out, and I'm not willing to lose message history (quicker and quicker as popularity increases). If someone comes in with an issue it sure would be nice to be able to refer back to the conversation when somebody else had a similar issue two months ago.
Also it's a lot of overhead to join a new slack group for a random comment. It makes sense for the discussion to happen in the same environment as the code.
We moved our community chit-chat to GitHub when we were invited to the Discussions beta. The main reason why I like it: It moves discussion closer to the code. Specifically it creates a nice swim lane next to `Issues`. I think of a progression of `Discussion` => `Issue` => `PR'. It gets discussion out of issues and PRs and declutters comments.
Just wondering, why did you choose Github to build your community? why not Slack!