I think it’s a philosophical difference that the Git maintainers likely have a strong position with. Some people like having one piece of software that does everything in an integrated way, and some people like purpose-built tools that focus on doing one thing well.

Git is a version control system; it’s not a complete project management solution. You can build integrated solutions around it, like GitHub, but if GitHub’s issue tracking is too primitive for you and you want to use Jira instead, that’s super easy.

I actually favor that approach myself. If I wanted to use Fossil but their issue tracker didn’t work for me, the best case scenario is that I just integrate Fossil with Jira or whatever and just haul around this vestigial issue tracking system that I don’t use. Likewise, if I wanted to use Fossil’s issue tracking but not their version control, what then?