They can, but not in this matter. They can only really hear an appeal of a state court when the state court has either a) Ruled on Federal law (which state courts can do) or b) Ruled on a matter in which state law or state case law is problematic to the US Constitution (usually, but not always 14th Amendment questions.)
There is a long-standing and very widely defended culture of case law that says that states are entirely in control of their own elections -- even Presidential ones -- and the US Constitution only permits Congress to alter their regulations concerning the time, manner, and place. Hamilton's dicta in The Federalist argues that Congressional alteration of state election laws was only intended as a way to make sure that states would actually hold Federal elections, not to insert the Federal government into state authority. The courts have generally honored that argument.
That is why the District and later Sixth Circuit US courts never ruled on the actual merits of the case: it was not their role to do so.
The ED of MI ruled on the merits of Stein’s case. Just because she lost doesn’t mean that federal court didn’t rule. The long hearing on Wednesday was to address her claims on the merits, and the opinion was on the merits.