in the current SW pc game Knights of the Old Republic (taking place some 4000 years before luke/anakin etc...), we discover that tatooine had been settled before but something happened and now it is settled again... how about this: the sand people are what it says - Sand People. they have been on tatooine for as far as records go, and they wrap themleves in sheets to protect them from the harsh environment that a desert planet is/can be. i could imagine that tatooine does have crappy weather cycles and those could be very harsh on people if they are not protected.