Ex - lots of refs are to "multi-arch" images, Except... there's no such thing as a multi-arch image, the entire identifier is just a reference to a manifest that then points to a list of images (or other manifests) by arch, and the actual resolved artifact is a single entry in that list.
But it means the manifest needs to be able to reference and resolve other names, and that means including... names.
For a more concrete example, just check https://github.com/moby/moby/issues/44144#issuecomment-12578...
Basically - the digests weren't intended to support image verification across repos, and the tool doesn't treat them that way. The digest was intended to allow tighter specification than a tag (precisely because a publisher might push a different image to the same tag later).