TL;DR
Imagine that you are an election observer. Can you certify any of the following?
Were impartial observers verifying signatures on mail-in ballots?
Did each party have equal access to provide information to voters through the media?
Were election laws applied uniformly for all voters in all jurisdictions?
Were ballot-counting procedures uniform in every city in the state? Were they monitored by independent observers at every moment?
Were ballot-deposit procedures transparent and uniform?
Can you certify that no extra ballots were introduced to the counting center from outside the normal counting process?