Early voting is one of the easiest ways to cheat. Just pay people for turning over their ballots, or intimidate them into doing so.
Protections exist against this at the polling place, but not for early ballots.
Somehow most of us managed to vote on a single day until 2000. I don’t see what that had to change. If Gore had won I’m sure to the elites the prevailing election system would have been just fine and things would not have changed as dramatically.