A git repo is usually shared over multiple machines/developers. So the chance of someone publicating it is larger. As well as the entire history is usually copied everywhere
All of these machines and developers have legitimate access to the secret in question, though. Hence my framing of git as just a file storage format—any other mechanism provides the technical means for any of these machines or developers to publicize it. (And a few other simple mechanisms, like "scp the secret from another machine" or "copy/paste it with your terminal", have an increased risk of doing so by accident. Accidentally making a git repo public is generally unlikely.)
Why would that be a general rule. I track my personal passwords in git (using pass). I'm the only person with access to that repo. I just like to have a history - and the convenient way of moving files around and merging changes.
