That would be my theory as well although I'm not sure it totally squares with the huge variations by country. [1] There is some alignment with Northern Europe (less UHT--less lactose-intolerance) vs. Southern Europe but even then there are outliers like Greece.

[1] https://en.wikipedia.org/wiki/Ultra-high-temperature_process...

UHT wasn't really a thing until the 70s. From the early 60s, Europe was booming and the war no longer had an influence on peoples' living standards (at least in the west).