Why github doesn't cache archives instead of regenerating them on the fly is unclear, and maybe something the developers should address. Or maybe there was a cache and it got blown away by the change that caused the archive checksums to change.
Github could just generate the tarball once and store it in the same way as other release artifacts. But for some reason they chose not to.
Once the accompanying gzip-version is sufficiently old or unsafe, breaking very old releases does not matter anymore, making it a seamless transition.
In my experience this sort of simplistic proposal by an outsider is almost always born of ignorance about the complexities of the actual system.