Sequioa Vote Systems (and Smartmatic) which is now Dominion
The AVC Advantage contains a computer. If someone installs a different computer program for that computer to run, it can deliberately add up the votes wrong. It's easy to make a computer program that steals votes from one party's candidates, and gives them to another, while taking care to make the total number of votes come out right. It's easy to make this program take care to cheat only on election day when hundreds of ballots are cast, and not cheat when the machine is being tested for accuracy. This kind of fraudulent computer program can modify every electronic "audit trail" in the computer.
Also, using different means allows them to deny coordinated effort.
I think whoever is pulling strings may have told key people in those states they needed to cheat and allowed them to use the methods they used historically and were comfortable with. Gave them the desired endstate and allowed the subordinate to figure out the best way to reach it.
I think the ability to switch votes with the software was a fail safe to use in an emergency if it looked like Biden wouldn't win. The jumps in Biden votes in MI and WI looks like a less sophisticated emergency action and they were just hoping the media would cover for them.