This looks like one of those cases where being a country of written laws can lead to weird outcomes. Yes, the right to vote should be universal. But, if the law, as written, doesn’t say that, then that’s not really the law.
Without looking deeper I all but guarantee that these are relics of Jim Crow or earlier. They are a disgusting stain on our country, but not nearly as disgusting as those who would try to leverage them in the modern era for the sake of dragging us back to that era.