It has a much more specific reason, I read. I read it originated at the end of WWII, when US GIs travelled around France and in Paris, and had their only real experience of people who lived under occupation for years. For, soap was rationed, with the German Army carting off production for itself; to boot, many people couldn't buy many new clothes and water for washing was also constrained.

_{*Lunatic*, n.
One whose delusions are out of fashion.}