Because people will delete and create new modes as they iterate so those hash links become stale. So while the person who replied to you is technically correct, effectively it is still very unstable.
I wish it was easy to grab a URL for that specific version, with a banner at the top saying it's not the newest version of the code (something I sometimes see with documentation). I don't see why Figma couldn't do this, too.
On GitHub you can hit the 'y' key[1] and it will add the revision into the URL.
GitLab will most probably have something similar.
[1]=https://docs.github.com/en/get-started/accessibility/keyboar...
https://docs.gitlab.com/ee/user/shortcuts.html#project-files