Deathfat's big skin folds happen because fat isn't taken away the same way it's deposited.  Your body doesn't know that your skin is now hanging to your knees.  It just is trying to distribute the fat evenly under the skin.  And as long as there's fat, the skin doesn't go back to the body.  There are people who have REALLY lost all the weight, and even their most stretched-out skin looks totally different than the thick folds, which are...mostly fat still.