I'm convinced that they wear ever more revealing dresses in the hope of getting more pics of themselves in the press, thus raising their own profiles and those of the films they're promoting.
One of these days, one of them will turn up wearing nothing but stripper pasties and a g-string, with maybe a few strands of chiffon or something in the hope of fooling people that it's actually a dress.
It's their choice, if they want to do it I don't really care. But then I'm not fussed about nudity anyway.