Well, in the earl 1900's it was deemed offensive for a woman to show her legs. Well, pretty much any flesh really. Times have changed, and now it's acceptable to go out bare legged.
Now then, for the science part.
Men are programmed biologically to go for youth. And if you look at the fashion industry for women, it's geared to make women look younger.
The make up you wear, it's to make your eyes look bigger than they are. Big eyes are a sign of youth. Lipstick, to make your lips look fuller. again another indicator of youth. Clear skin. well, you're getting the idea about foundation, concealer, and most of all "photoshop". :)
With regards to hairless legs, well, isn't that also a sign of youth. Likewise with armpit hair.
As for Brazillians. Well, I think that is pushing the jailbait look a little too far. But in essence, that is what the fashion industry is pushing women towards.