I have a feeling that a lot of them believed their own bullshit polls and thought Biden would win in a landslide. Once FL, OH, and IA were called, and MI, WI, and PA were looking really good for GEOTUS, they slammed on the brakes and realized that they had very little time left to "fix" this. So they got sloppy and did a rush job. That can be seen by the sheer number of votes for just Biden but nothing down-ballot. It can also be seen by them only ejecting poll watchers later on in the day when the really intense fraud started.