Comment by ericzundel

I was thinking that Japan and Switzerland likely have good rail networks because the buildable land is severely constrained by geography. In those cases mountains, and connected only by thin linear corridors (valleys and near coastlines). Look at this map of Japan: The green areas aren't just natural areas, they are too mountainous to build cities.

https://www.eorc.jaxa.jp/ALOS/en/dataset/lulc_e.htm

In other places with large, flat expanses, human civilization spreads out to an extent that expensive railroads just can't serve the needs/desires of people. You could artificiallly constrain it, but you know what? People in general just don't like being told what to do.