[BenOfTomorrow]

I bet a lot of people would use the same key to open all those places if it were actually a plausible option.

That said, physical keys are different enough that an analogy breaks down. They're much easier to circumvent (break a window), while their use by a thief is much more impractical (finding the lock and avoiding detection at the location). Criminals in possession of your physical keys will be local (or irrelevant) and limited in numbers. It's easy to get back in your house after a criminal has entered.