What makes you think these states only developed after WW2, and how does this explain the US having the world's best passenger rail system in 1920?

Here's a map of it; see how densely it links up this vast country: https://vizettes.com/kt/rta/maps/usa-rr-1920.gif

Meanwhile, the Netherlands was completely car centric just like the USA until the 1990s, when they decided to start redesigning roads to prioritize walking and cycling. Are you sure these things are really inexorably linked to geography?