"overworked or incompetent election supervisors"

Well, incompetent is a subjective kind of thing, but "overworked" is I'd suggest a key elemetn here.

What seems to keep coming up are indications that these kind of problems are prevalent because people are trying to cut corners and do it in the cheap. Not having enough people to do the counting, so that mechanised systems have to be used, and a manual recount is a big problem.

Then there are reports about how poor counties have inferior machines, and about places where there aren't benough voting styastions and voting booths, or not ebnough people to process the voting or advise the voters.

And this is in what is far-and-away the richest country in the world, where incredible sums of money are spent in the course of the elections. But not on the things the money needs to be spent on, not on ensuring that it is fair and efficient.

It is like that not because of some inevitable difficulty in conducting elections in a big country, but because important people have decided that it doesn't really matter, so long as they can get elected.

It seems pretty clear that the people in charge don't have much regard for the ordinary voters. Which is consistent with the way this whole thing has been discussed with the focus on the rights of the candidates, as if that was what really mattered.