Hard to say. Maybe the technical and/or manpower limitations when the designers made those armors and textures where just too constricting to allow better designs - or designs I like more, to put it another way. I really don't like any of the older sets/armors, just too blocky for my taste.
But I would love some tacky, well designed Bikini, or a short skirt with a hot top ;-). As long as it fits the character and is high-res / high poly.