There are remote and difficult to get to areas of Europe as well, by the way.
The social policies espoused by the SDs arose more from class conflict, which we had here as well, than from the world wars. The world wars acted as a catalyst for the SDs to get political agendas passed. The US would probably have followed Europe’s path more closely but for the fact that we were flush with Western European money after two world wars, and the unions could get a hefty pay raise. That kept the pot from boiling over for 20 years. Then, by the early 70s when it looked like we were about to implement the full SD monty, we hit the oil crisis. Our budget has never really worked since.
While Western Europe has its rural areas, the diffusion of people is much more uneven in the US. Texas alone is about the area of Austria, Hungary, and half the Balkans. North Carolina is about the size of England. A much higher propoportion of Texans and Carolinians live more than hour from a city than Austrians or English do.
According to the last census, about 1/4 of the American people live in the boondocks. That’s around 75 million people. We are bleeding money trying to support those communities. If we attempted to run a national health service along European lines, it would be a disaster. Canada’s health care system is straining for the same reasons. Same in post Soviet Russia.
Big countries are great at some things - Germany could handle Britain and France, but was done for once the USSR and the USA fully marshalled their forces. Who doesn’t want a giant on his side?
There are serious inefficiencies, also, which result from the requirement to duplicate effort in so many localities. The state - run school systems in the US are another good example, along with the rail roads. The quality gets very uneven the farther one travels from civilization.
Theoretically, we could fix some of these things but we would need to amend our constitution to do it. At this stage of the game in the US, that is just politically impossible. We can’t agree on a budget we can’t even begin to balance.