Because the six disputed states (Arizona, Georgia, Michigan, Nevada, Pennsylvania, and Wisconsin) ran entirely fraudulent elections
Yet the supreme court wouldn’t hear Trumps case looks like not just the elections were rigged huh?.
Plenary powers exist between the states' legislatures and Congress to deal with election law and politics. That excludes the Executive and Judicial branches of government, by design. That's why the way to remove an elected officeholder is thru a quo warranto (by what authority) court action. The officeholder has to show the authority behind an action they took. The court setting allows evidence to be presented and a finding of fact. I can understand the Fed setting would allow the decision to be binding in all states. But elections are about politics, not law, so courts have no power of resolution. That is left to Congress.
If an election was held according to election law in the state at the time (and necessary referendum was done), then the election was lawful, and conferred the state's authority of the office to the officeholder. Winner - officeholder.
But Wait! The Referendum required by the State's Constitution was not held, even though passed by legislature and signed by governor? Winner - challenger,
and a thankful nation has its first UNLAWFUL 2020 election.
IANAL - I am not a lawyer