Can it be this simple?
Theory:
They preprint a bunch of ballots with the Presidential choice already filled in.
These are typically forward to the precincts where they are required and local officials fill in the down ballot votes.
Because of the overwhelming win, they had to rush to get them through the counters and didn't have time to fill in the rest.
This would help account for the high number of Biden only ballots.
It seems reasonable that the automated fraud would include down ballot votes.
Next question
If the vote count is manipulated via the Dominion machines and 100% manipulated, why bother with fake ballots, "lost" thumb drives etc?
A:
Recruitment.
Even electronic fraud requires some human cover.
Without dishonest people in positions of power in key districts, the manipulation would be obvious.
The physical fraud is a means to recruit crooked people into the positions that oversee the vote count. A person who agrees to "misplace" a thumb drive in an unimportant county is a candidate for a bigger job next time. That position would require a little larger fraud.
The election supervisor in Floyd county GA was probably about to get an " unrelated" job offer in a larger more dimocratic county. Essentially, it's grooming and takes place over a period of years.
It's a tried and true system that works in a broad array of industries.
Surely you don't think that 93% of news actors self identify as dimocrats by accident.
Advancement requires compromise.
Be compromised, or you won't advance.
Valid point.
They fucked up last time by relying mostly on machine based fraud and doubled down on the physical fraud this time but it still wasn't enough and they ended up with lots of trackable anomalies.