It's not too difficult for Americans to understand. We just didn't want their system.
I sad "Difficult for Americans to comprehend." it's easy to understand for sure, but if you tell an average American, "Hey it's 87 kilometers to the next town," they will look at you like you have a horn growing out of your head, because they have no idea how far that is without knowing the conversion factor and whipping out a calculator.
So yeah... It's difficult for Americans to comprehend distances and measurements in metric.
Most engineers and designers I have known would have loved to switch over the the metric system years and years ago. And yes, it's a better system than what we have by any measure. (No pun intended.) The average person just simply does not like change, because they have to learn something new. That's the reason we don't have it.
