Dress for success...

I will begin this by saying that I enjoy dressing up and looking nice. In fact, I think it would be nice if people took a little bit of extra time to look nice, instead of "cool". Sure, I wear blue jeans and t-shirts as much as the next person, but I still appreciate the early part of the last century where everyone - literally everyone - dressed up at all times. Men wore suits in every situation and women wore dresses.
I want people to be comfortable, and I'm not going to tell anyone what to wear, but a sharp three-piece suit and a fedora looks a lot nicer than a pair of skinny jeans and a flannel. Hell, even middle class and poor people back in the day wore suits; they may have been lower quality materials, but they still wore them nonetheless.
With that being said, I cannot figure out this need in the modern workplace to dress up. Sure, if you meet with clients all day long, or work in customer service in general, I can understand the company wanting you to look professional. However, when I work in a cubicle all day long seeing no clients, and our office in general recieves visitors only few and far between, I cannot understand the need to wear slacks, a shirt and a tie.
I was told once that I should "dress for the job I want, not the job I have". Alright, I get that. But it still doesn't explain why the job that I want requires me to dress up any more than I do in my current job. Couldn't the job I want just as easily be a job where I can wear jeans and a t-shirt, instead of dress pants and a button down?