because the "One Size" only pertains to average sized women, not plus sized women, unless you have really skinny legs. They would not stay up for me and after washing and drying them they have shrunk so mush that I will have to give them to one of my young neices. Also, I found the material to be too thin and therefore, they were not warm. A big waste of money for me and if you have chubby legs or have really long legs, stay away from these.