Look at his knees, his posture. He's straining to not lift, but drag this thing across the ground. The point furthest away from his hands' grasp is held up by the strength of the fabric, this is a heavy object; clothes are malleable and are easily shaped. There wouldn't be uniform formation in the sack because the clothes would just tumble around (but would eventually settle, sure). Whatever is at the furthest end though is heavy.