By that same argument toenails should be arousing to most. The point is that it isn't the legs or hips or butt. Feet tend to be dirty, the smell is not attractive to most people, and the appearance is off-putting to many when it becomes a center of foucs because they appear as malformed hands (which they kind of are).
If you argument held much weight the entirety of the lower half of a woman would be focused upon but it isn't. It is almost exclusively tailored to the feet themselves even if the rest isn't visible.
