 Why do the webfoots only wear skirts?
A gray, funnel-shaped cloud of dust stood off to his left. Weather control made cyclones and other climatic phenomena on earth practically non-existent. The sun burned fiercely, although he would have said it was about four o'clock in the afternoon, if this had been Earth. But then, how could a group of loosely spaced grains of sand possibly have a nervous system? When it changed to a cube he drew a square, a circle for a sphere, and so on. He became so absorbed in doing this that he failed to notice how the wind devil drew closer and closer, but when he inhaled the first grains of sand, the realization of what was happening dawned with a flash of fear. These creatures were not only humanoid, but definitely human, although more slight of build than earth people. All were dressed from the waist down only, in a shimmering skirt that sparkled as they moved. The men were dark-skinned, the women somewhat lighter, with long flowing hair, wide lips and a beauty that was utterly sensual. They had exhibited human emotions of anger, fear and, that most human of all characteristics, curiosity. But up to now the tube and the chain was the only evidence of an advanced technology, unless the ancient inscriptions in the stone wall of the pool, and the statues lining the wall were evidences. An object like a pallet was brought, carried by four of the women. There, at the cavern entrance, the wind devil writhed and undulated in a brilliant harmony of colors. One of the women came toward him, long golden hair flowing, firm breasts dipping slightly at each step. It is impossible to move a physical body from one place to another by a mere thought and a tiny instrument, yet you have done so. These are the undesirables, the incorrigibles, the nonconformists from the sixth planet. There are these web-footed people, who were hostile until they thought I was a God. The tube these webfoots use is a toy by comparison. And this is contrary to the greatest law of all—that an entity, once in existence, can never cease to exist." "As for the webfoots," the wind devil, or Sand God, said, "I will destroy them. They exist, therefore they always will. It has to do with what comes after physical existence, not with existence itself. The greatest law is this, that an entity, once existing, must not be harmed in any way. To do so changes the most basic structure of nature."
 The Sand God burned everything, except for the skirts.
 Skirts are traditionally worn by prisoners. The webfoots on this planet are all criminals or descendants of criminals.  The people from the sixth planet only sent skirts, when it was communicated that the Sand God had burned everything else.  The Sand God burned everything, except for the skirts.  Skirts are the traditional dress for the webfoots culture.