How do you count a smudge instead of a complete filling-in of the oval? You have humans go over them, and people hate that.
Just because you never see this issue doesn't mean it doesn't exist. It's just that the ambiguous ballots don't matter in the vast majority of elections so no one cares.
I'm not saying computers are better than paper. They each have trade-offs.
There's never been any real discussion about it being complicated, confusing or needing any other kind of design change. (Which isn't to say that you couldn't make arguments in that vein.)
It just seems more natural to fill in a line than to fill in a circle. Your wrist is more stable and less shaky to make a couple straight lines with a marker.
I was going to say you're wrong, but I agree that if I had to fill in dozens or hundreds of items, I'd prefer filling in lines. Your wrist is more stable and it seems like a very quick motion.
However, that kind of efficiency isn't required at all in a ballot. Making a couple of crosses instead of lines isn't going to make a big absolute difference in terms of the entire voting process. You want to maximize other things, first and foremost making it easy to understand and easy to recognize clearly for both the voter and the people/entities who count.
Just because you never see this issue doesn't mean it doesn't exist. It's just that the ambiguous ballots don't matter in the vast majority of elections so no one cares.
I'm not saying computers are better than paper. They each have trade-offs.