GitHub is actively used to do code review and bug tracking. There is a number of tools that offer it on top of git, in a distributed way, but it means that yo need to install them locally on every machine involved.

What's worse, GitHub is widely used as a CI/CD solution, it runs massive amount of build pipelines and test suites. There is a ton of players in this space, too.

GitHub's main value proposition was having all these things in one place, as a convenient web app, for free or for moderate money. So they're crushed by the success of their model.