You are making the common mistake of assuming that the US political system works similarly to the standard modern democracy found in Europe and parts of Asia.

You are making the common mistake of assuming that the US political system works similarly to the standard modern democracy found in Europe and parts of Asia. It doesn’t. It is infinitely more deadlocked and slow-moving, mostly by design. Switching to metric wouldn’t be a matter of “a politician” proposing it and 50%+1 of the parliament agreeing. It would be a massive, years-long all-consuming struggle.