Because it is easy to see how in a single case a paper and pencil vote can be cheated. Switching votes, a bad counter, throwing away some votes from the guy you don't like... all of these are easy to imagine. In comparison, the types of attacks needed to take out a voting machine seem much more complicated. And so many people seem to assume that this means that voting machines are more secure.
In my own experience, most people who view it this way don't consider scaling. While pen and paper is an easier attack for a single voting station, it is far more difficult to scale. Every voting place brought in on the scheme has more people who could be caught or decide to go public, and that is assuming you are able to get in contact with those people in time to ensure they are able to intercept the voting. With voting machines, one good exploit, especially for wifi enabled machines, can easily infect larger numbers.
As to why other countries don't have people viewing it this same way... I don't think it is because they have better ability to consider scaling attempts to exploit a system.
In my own experience, most people who view it this way don't consider scaling. While pen and paper is an easier attack for a single voting station, it is far more difficult to scale. Every voting place brought in on the scheme has more people who could be caught or decide to go public, and that is assuming you are able to get in contact with those people in time to ensure they are able to intercept the voting. With voting machines, one good exploit, especially for wifi enabled machines, can easily infect larger numbers.
As to why other countries don't have people viewing it this same way... I don't think it is because they have better ability to consider scaling attempts to exploit a system.