Who wouldn't like to have smooth, blemish-free buttocks? The skin on our backside isn't any different from the skin on the rest of our body. As much as we think it's less 'vulnerable' than our face and other parts of our body, it does go through things that weaken it.
For example, sweat, constant friction with all kinds of fabrics, the big contrast between receiving no sun in the winter and an overdose of it in the summer, etc. Therefore, it is not unreasonable to think that you may need to pay a little attention it.
However, these are not miraculous masks. As with facial masks, you'll get better results when you pair them with good hydration and nutrition. If not, they will be useless.
Remember that masks are meant to treat the skin... stretch marks, sagging, etc. There are other ways you should to pamper this area (gym, squats and diet, you already know...).
Want to know about the best butt masks? Click on the video.