China has a working HSR system connecting all their major cities. The fact that their population scale is so massive means they also try weird shit to get what they can.
Japan is very narrow but it’s also very long. The actual amount of miles a train much cover from one end to the other is very large.
Yes the EU is not one country (though it is a polity). That should make it harder, not easier to cover it with rail, and yet there’s rail lines connecting all the major cities crossing national borders. Does the “size” counter reset once you cross a line on the map?
It’s not the size, it’s the political organization. You even hint at this when describing how we paved America: the political and economic configuration was aligned to make it happen despite the massive cost. The USA was crisscrossed by passenger rail and street cars, and still is for cargo. We just took a different path later, but it doesn’t actually have to be that way.