[zygentoma]

Because you would not want to write the whole git history starting from the commit you want to stash this info one everytime you want to stash additional info …

Appending information to the commit itself creates a new commit and all the commits that are based on the commit will also have to change consequently.

[827a]

Ah; so notes don't impact the commit hash? That is a solid reason.

[cesarb]

Yeah, git notes are AFAIK stashed into their own hidden branch, referencing the original commit by its hash. That is, the git note points to the commit, not the opposite.

[Izkata]

Kind of. The structure is the same and you can check it out if you want, but it's actually a 3rd directory under "refs" - the other two being "heads" (branches) and "tags". That avoids special-casing with trying to hide branches or conflicting with a branch name a user might make.