I've only had one pair of Levi's in my life, I won a pair of them some 40+ years ago. What happened to them was the same that seems to happen to all my jeans: They wore through right below the back pocket. As far as I understand it's the thick seam of the pocket that either slowly grinds the fabric or stiffens the seam area so that stretching caused by sitting down is concentrated below the pocket instead of being spread to the entire rear.