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Cheating takes some finesse. You don't need to cheat if you are winning. That’s the purpose of delayed ballots, whether it is ballot harvesting or mail-in ballots. You do as much cheating as you can without being obvious up till election day. If you are still losing at the end of election day, you probably have a good idea how much more cheating you will have to do in order to win. You just want to do enough to win.
If you are behind by 100 votes, you can find 100 votes for your opponent, and 201 votes for you. Not too obvious.
If you are behind by 10,000 votes, it gets more difficult. You might have to find 200 votes for the opposition, and 10,202 votes for you. The wider the margin on election day, the more obvious the cheating becomes in the following days.
But they are without shame. If every single ballot they find after election day is for Biden, they will do it with a straight face, outrage at any questions, and an army of lawyers to back them up. Lie, cheat and steal. They even say it out loud sometimes.