They can. And they should. But state election law changes are subject to approval of Congress.
Not according to the Supreme Court.
And I’m pretty sure that the states make up their own laws. Issues in the past have been things like Congress meddling in state elections and election laws and the lawsuits that have arisen from them that ended up in federal court, for some reason, even though they’re state issues.
But, feel free to show me where the US Congress has jurisdiction over state voting laws. Unlike others on this site, I don’t have a problem learning something new.