Having maintained private versions of Debian packages, I have zero need for "commit messages on changes to patches". I can diff them as needed as I showed, but I rarely ever need to -- I mostly only rebase onto new upstreams. Seeing differences in patches isn't helpful because there is not enough context there as to what changed in the upstreams.

I rather suspect that "commit messages on changes to patches" is what Debian ended up with and back-justifies it.

Of course, I am not a Debian maintainer, so it's entirely possible I'm just missing the experience of it that would make me want "commit messages on changes to patches".