Comment by deathanatos

My best guess is that the commit metadata (particularly, message) is missing. You could always have it be "(uncommited, staged changes)" though, and that's probably descriptive enough. (I agree with you on the whole: having the staged data be a commit makes things conceptually much simpler.)

My other guess is that the "index" (the other name for the staging area) is also used for conflicts during merges & rebases, and that somehow plays into the problem of making it an actual commit. (But again, this comes across more as an excuse than a reason: I don't any viable reason why the staged changes can't still be an actual commit, and the merge conflict data just stored as a separate structure.)

That, or the person who added it just didn't think of it, or couldn't do it due to backwards compatibility.