Perhaps you'll prove me wrong in a follow-up comment, but in my experience folks who think about paper vote fraud like what you describe, usually have little to no experience at actual polling places aside from popping in briefly to vote.
In contrast, you could have 20 people looking at an e-voting machine, and none of them could tell whether it's working correctly. It's a black box, literally in many cases.
For example, maybe rural counties are more likely to use paper ballots than urban counties. (Or any other variable: income, race, geography.)
Project Veritas is not a credible source.
Edit: It seems like HN has gotten a lot more Trump and conservative since the election. I should hope that reiterating that submitting thousands of paper ballots of a lot more complicated than hacking into a computer system is obvious.
I get that this is a tech site, and we like to think that everything is the result of smart hackers (even the Trump election! because some Russian hacker could be the only explanation), but there are low tech options here as well.
The Project Veritas videos, whatever you may think of them, had high level operatives openly discussing tactics they use to affect elections. A few extra paper ballots seems like something a motivated person with access to a photocopier could accomplish.