The code itself doesn't even contain much of the information relevant to coders, you'd have to also look at the git repo, its history, its commits, etc.
The code, or the repo, however are in most cases not the source of truth for a business roadmap, prioritisation discussions, estimation, customer feedback, bug reports, and so on.
It's a myopic view to only look at the code without any of its context and conclude that it's "the" source of truth.
Also, I don't know about you, but most places I've worked haven't struggled with keeping the code and JIRA in sync.
