Women have to follow these rules because they want to and not because they are being forced to or because they are bombarded by signs. Also because the choices they are given are pretty and flattering.
The options they have available to them need to be stylish and exciting. If the clothing that bombard them when they enter the stores are fashionable, exciting but not quite what the Rabbi ordered, it makes it very difficult to do the right thing. Especially when the sales people tell them “everyone is buying them, its all the rage. You can always take it to the dressmaker to add to the hem, etc.” But when they go to the dressmaker, she tells them, there is nothing to let down, or if you add a piece it will look awful and it is fine the way it is, everyone is wearing it this way. And if you try to return it to the store, they won’t take it back and they again reiterate “it is fine, everyone is wearing it this way”.
I am really sorry to say that the stores need to be held accountable and need to take some achrius here. Frum owners know exactly what they are doing when they bring these skimpy outfits into the store. They know exactly what they are doing when they make their suggestions how to wear them and add a tee shirt or let the hem down. They know exactly what they are doing when they ooh and ah how cute these items look on their clients and how they “must buy them”. They are promoting these non tznius looks just to promote their bottom line. It is easier to buy these available looks and not do their homework for the Frum consumer. It is easier to get the Frum consumer to buy these looks than to work harder to find the appropriate ones.