UK population density (people/sq km) is 289 and Switzerland's is 228, so not very different. Plus Switzerland is fully connected, there are no remote islands.

[1] https://www.worldometers.info/world-population/population-by...

Australia also has paper ballots.

The area isn't that much of a problem

So more populated countries have more potential poll workers to choose from. Isn't this a linear relationship? What does size have to do with anything?