1) Florida's AG (or SOS, as it is in some states) had certified the results as Bush winning.
2) Florida's legislature didn't step in and stop it. Since the legislature didn't invoke their Article II privilege to choose their EC electors, the assumption was they agreed with the AG's vote tally -- Bush got the EC votes from Florida.
If my memory of that SCOTUS ruling is correct, applying that to today would mean silence from a state's legislature is seen as agreement with a state's AG for how the votes are tallied.
And if the state legislatures choose a separate slate of electors, if they are tied up in the courts by Dec. 14 wouldn’t that mean no electors have been chosen since it wasn’t done on time?