Never heard that theory but it makes sense. I just assumed they were denser and liked digging tunnels more.

That’s a contributing factor. Their land mass, topography and general population density benefitted it highly as well, but the need to reconstruct their cities provided two problems that needed solving - fix the previous infrastructure and get the workers from outside the demolished zones into them. Trains existed for a lot of things already so it made sense to keep pushing them into the city centers. It was an inexpensive and reliable solution.

We better get flying trains after this one

ww3 involves nukes, i doubt very much infrastructure was left by the time it ends.

Perfect opportunity to build from scratch.

And that means what?

I’m not familiar with that theory, but Europe has been building a robust public transit network since the early 20th century. The wars only slowed progress. Most Subway systems, rail networks, city buses, etc were quite strong already in the 30’s.

They had it, but WW2 did so much damage (WW1 contributed to this too) and the need to move workers around cheaply and reliably to rebuild gave them an opportunity to improve public transit and make it the primary focus for transportation infrastructure. Build the transit route into the communities or commercial areas, then rebuild those zones around it. By the 70’s it was fully modernized and a primary focus from governments. Without that destruction it may have just been city centers like North America does.