It was what was presentable at the time, and these people knew they were going to be photographed or filmed and likely the whole town would see them so they dressed up lol.

I've worn sweat pants outside my house maybe twice in the past decade. Once was the day after a surgery on a cyst and I couldn't wear a belt. I like button up shirts, but I need tailored ones. I'm a bigger guy, and work in the trades. I can hulk rip out of the cheap ones you can grab from Walmart etc. It was probably different in the 40s when your average man had muscles rather than office worker twig arms and dick wrists.