I say this as a veteran of a time when women began to enter the professions in the US in larger numbers and there seemed to be an expectation that we dress as prison matrons from a 1940s movie, lest someone notice that we were indeed women
I'm only in my 40s but I think this is so true. It's only in the last 5-7 years that I've felt comfortable not wearing a suit day in and day out. For years in the City, that was my uniform - trouser or skirt suit with blouse/shirt/silky t-shirt underneath. Even when I worked in a more casual environment before that, I would have felt obliged to wear a jacket at all times.
I've just bought a dress (from Sainsburys of all places) with a collar and I am looking forward to wearing it next time I go into the City on a nice day. No jacket required. I do still tend to wear jackets with dresses but that's more because I am [coughs politely] large of bust and feel more comfortable usually. And I get cold easily. If I'm wearing a skirt/trousers with a nice top, I don't necessarily bother with a jacket at all.