Believe it or not, you're not the first to think about this, it's called the American Disabilities Act, and it contains thousands of rules on everything from how heavy doors can be to the height difference between steps and where to put an elevator. The problem is that infrastructure that was built before the ABA was passed was grandfathered in, and doesn't require any change unless there is a major upgrade. So all of our old infrastructure is often sadly inaccessible.