I think there's also something to be said for the release tarballs being reproducible, since we have git there's not much reason not to. Some release processes have codegen and cleanup steps involved before the release tarball is cut from git, but those can be made deterministic and verifiable
I'll add that, on behalf of distro maintainers everywhere, we don't really mind running autoreconf or whatever against a raw tarball fetched from a git tag, as it were, and dealing with these codegen/release prep bits ourselves as a part of the package building process.
Perhaps we should be fetching git tarballs and doing this work ourselves unilaterally rather than relying on upstream-prepared release tarballs anyway? The target audience for those is the casual/ad-hoc builds anyway.