I'm really not sure why the popular thought today is that EVERYONE had a hat on their had in the 1950's. In most pictures and movies I've seen, it's really only older men that are, and they're probably holding on to their old hats, from when they were made well! Younger men were already revolting against hat-wearing in the 1940's, because they didn't want to ruin their cool haircuts with a hat.
The decline in hat-wearing started a decade earlier in the UK; I cannot remember my father (died 1962) ever wearing a hat (he might have done before I was born)....by the 40s hat wearing had already been on the decline in the US and by the 50s was pretty much a decaying industry ...