Rob
It was always the style even by non Jews to wear long skirts often to the floor. Lack of modesty in dress was quite rare in the 17 and 1800s as well as the early years of the 1900s ever see the pictures of old times or even the beginning of the 20th century? There was no need to focus on that aspect of tznius because it wasn’t an issue. There may have been other issues like not covering hair by some parts of Klal Yisroel but I don’t think anyone ever wore a short skirt. It was probably illegal. I remember hearing that in the 50s if you showed too much skin you got a ticket so I’m guessing it used to be stricter back then. Either way I never came across this sefer lamenting the short skirts that the women were wearing. However there were other issues.