What was apparent before election day was that Dems would dominate the mail-in votes, which in many places are counted after the day of election votes.
Exactly how/when mail in votes were cast varied from state to state.
In Georgia, there is no such restriction. Absentee ballots are counted the day they are received, and the totals are kept secret until election day. Normally, the absentee ballot totals are the first ones thrown into the tally. But in 2020, they kept adding more and more each day. Dekalb and Fulton, and Gwinnett counties announced more than once that all ballots had been counted, only to come up with more votes the following day. Fulton even announced that mail-in ballots were still coming in, even though there is a strict election day cutoff for this. Of course if Trump had any political sense at all, he could have filed suit and stopped it in its tracks. But he didn't. He figured holding a rally was just as good or even better. Surely, if corrupt-as-hell Fulton and Dekalb county Democrats could see the size of Trump's rallies, they would submit and declare Trump the winner.
Also, there is that matter of Facebook and Dominion money that Kemp and Raffensperger got a big chunk of. Wouldn't want to jeopardize that by enforcing election rules.