Why is forking only available for Mercurial repos and "NEVER" for git?

[systemapproach]

Atlassian Documentation states the following on forking repos:

Choose at what point in the code to fork the repository. This option is only available for Mercurial repositories that have one or more branches, tags, or revisions. This option is never available for Git repositories.

I'm trying to find out why forking is never allowed on git and whether I should just give up and migrate to github or similar.

[Nic Brough -Adaptavist- · Accepted solution]

Git doesn't have "fork at", you get the same effect with just "git clone"