to understand why the CanCan is considered disreputable, you need to understand clothes..

back in the days of full skirts, and no rubber or synthetic for elastic, woman wore an undergarment, pantaloons, that sort of looked like a loose pair of knee length pants.. only the crotch seam was not closed--except it the very front.

Starting about where a men's fly (Zipper placket) ends, the crotch seam was open to the back. the garment had a drawstring, and tied on, in the back-- it was the wearer responsibility to make sure the sides of garment met at the draw sting.

This kind of underwear mades sense-- with a full skirt, it was not convient for women to pull down their panties (pataloons)-- remember to do so, they would have to untie them! With the open crotch, they could just pull the garment aside to respond to calls of nature.

In the CanCan, the woman flashed their skirts up, and kicked up their feet, and as they did so, they often gave others a glimse of their underwear- and many a time what was under their underwear!-- shocking indeed!