When you support yourself day in and day out with the wrong shoe, your back has to work harder to pick up the slack. The average person is a heel striker which sends up vibrations to the knees and back. Since the knees work harder than normal, the muscles in your legs work hard and develop. From there, the average person does little to no exercise to stretch out the muscles, especially the hamstrings which when developed and tight pull on the back.
Then there's the simple fact that we have five toes which normally would be spread apart and help with balance and agility. We then shove them into badly fitting shoes and we squeeze our toes together practically forming one giant toe. This of course due to the fact that humans as a race decided walking on concrete and asphalt was much better than grass and dirt.