These stocks are some of the best thought out/ergonomicly designed that you'll find. There isn't much room for modification, or a need for that matter. What could anyone possibly want to change/modify? As for painting it, to each their own I guess. However the finish on these stocks is excellent and since most of them are ordered new for the customer in particular, you pick the paint scheme you want so I doubt many people would have a need to change it afterwards.
People buy this stock so that they do not have to make modifications.