Nude is versatile. It's not so much that I "prefer" nude, it just happens to look good with 90% of my outfits. Nude also does not require any color matching with respect to the rest of the outfit, as well as allows the natural tone of the legs to be showcased without disturbing the color balance of the overall outfit.
Black is also versatile. With a cocktail dress, it can be provocative; with an evening gown, it is classy and elegant. In all areas in between, it can be used for more modesty or to look more sexy. It can also be used to lengthen the legs, to slim the legs, to focus more attention to the top, to accentuate lines, or just to match the outfit color in the absence of any other hosiery shades.
Thus it is not necessarily a preference for nude or black; the fact that they are the most versatile naturally means that they will be used the most often.