So we don't have any aging infrastructure? No bridges that are well past an age that anyone ever anticipated? Maybe in your region, but a wood structure built on wood piling in the 1940s in Montana has exceeded it's life, plain and simple. And no joke we design to anticipated use and sometimes don't have a crystal ball. I never once implied that your two reasons weren't valid, but don't even try to tell me that we don't have aging infrastructure in many cases.That's not true at all. We design for specified loads, environments, and life cycles. The problem with the crumbling infrastructure is by en large two parts. Part 1 the infrastructure in the majority of these cases are working beyond what it was designed for. The reason we don't have cars that last forever is not because it's not possible, it's because it would be to d**m expensive. Part 2 future environments are not always foreseeable. It's one of the many reasons we design in margin.
I've no idea what your cars that last forever comment has to do with aging infrastructure.