Talk to Me Like I'm Stupid: Victorian Fashion

Less anyone think that this Jane Austen binge is somehow separate from my ongoing Civil War binge, let me say that I came to Austen to watch a writer negotiate a bound society. That Austen is critiquing these bounds through comedy--as opposed to tragedy--is interesting, and I plan to return to the subject. But that aside, in terms of gender, there seems to be something particularly bound about antebellum America. Perhaps this is a bad comparison, but I was watching the BBC's adaptation of Pride & Prejudice and was scandalized to see so much cleavage. Pride & Prejudice takes place a half a century before the Civil War, by which time--from what I can tell--"ladies" were much more covered, and they basically didn't exist below the waist.
Also the men of the Civil War period weren't really into fashion, in the way they would have been a century before. I took a tour a few weeks ago of the museum down at the Fashion Institute of Technology. One of their exhibits discusses how men of the mid-18th century favored black and fashion came to be seen as something for frivolous ladies. This from people who, only a century earlier, were wearing wigs and all sorts of vibrant colors.
Put simply, what happened? Readers of the comment section--though not observers of my daily dress--will know that I actually like fashion. In addition to seeing it as art, I've always thought of it as an extension of anthropology. If you have any sense of the historical, or economic, or social forces which would have caused the change please speak up. I'd love to read.
As always, please no shouting from the back-rows. There's nothing wrong with being dumb along with the rest of us.