A lot of this will seem trivial if you haven't used Github for an organization's management of issues. This also lets you start off with a markdown checklist, and convert items to sub-issues.
See, but I do. For almost a decade, we have used it as-is for tickets and bug tracking, and it's never been a problem. I just don't see the use case for sub issues.
Wasn't that already possible with Tasklists? We did it using "- [ ] description", then clicking the covert-to-issue hover option.