Humans are harder to compromise at scale. A single exploit can be replicated against hundreds of thousands of machines without heightening the risk of discovery by that much. Compromising hundreds of thousands of human vote counters without getting exposed due to a mistake is harder... although not impossible (it's in fact standard practice in plenty of countries)
Thats pretty much how they do it here in Canada. One member from each party plus an Elections Canada official. The ballot box is sealed in front of at least two voters , who determine that it is empty before sealing and then sign the seals. ( I know this because I was so early to vote the last election I had to wait for another voter to show up).
I can only talk about Germany. Election helpers are sourced from the population of the community where the vote is held. (You can be compelled to do it if there are not enough volunteers), at least two election helpers have to be with the urn at any time. Anybody is permitted to stay in the room from the moment it's checked that the ballot box is empty until the vote result is announced. The vote itself is made in a way that loudly announces each individual count.
Afterwards the result from every polling station is posted online. So if you want, you can make sure your vote is accounted.
Now I'v been an election helper since 2009, I've never seen anybody stick around for the vote. It's mainly the election helpers keeping each other in check.
Last time with the European Parliament elections in the Netherlands, there was a small uproar because the elections were held on Thursday (all other elections here are held on Wednesday), but the results could not be announced until Saturday or Sunday because most other European countries held their elections then. However, keeping the final result undercover for a few days is actually against Dutch election rules.
So, a critical web site organized a nationwide system where people could sign up for their polling station, to stay around during the counting and then report the results back to the web site. They got about 70% coverage I think; in the large cities it was near 100%. It was quite interesting. It was a close vote, and their result was slightly off, but close.
I am considering to alternate each election between being an official election helper and unofficial self-appointed monitor.
Depends on the country, here in Denmark members of different parties are counting the votes. So they have every reason to keep an eye on the person next to them, which is from a different party. Also the votes are recounted by multiple different people.