Actually, there is causation.
City dwellers walk more than suburb dwellers, and are thus in better condition. Of course, once upon a time, the opposite was the case. Studies done by the army in WWI showed that country dwellers were in much better shape physically than city dwellers (farm work builds muscle!).
So if you REALLY want to get in shape, live in the country, and adopt the lifestyle of a farmer from 1900.
Where is there hard data to support that thesis?
Not WWII era but anything recent.
In the USA other than Manhattan and San Francisco I don’t even see anecdotal evidence that is correct.