Quit being dishonest. You're not trying to understand because it's really fucking easy to understand.
If you really truly want an answer, it's relatablity.
If you ask the vast majority of Americans how many centimeters are in a foot, you'll get blank stares. If you ask them how long 30 centimeters are you'll get blank stares. If you ask them how long a foot is they'll hold up their hands about a foot apart.
Americans use imperial units because it's what they used daily, what they're familiar with, and what they know. It's really not that hard to understand.
Think about if you had to switch from Metric to Imperial. Just think about all the wonky units and how overwhelming it would be. That's how Americans think about the Metric system.
But it's easy you say, everything is 100 up or down. So? That doesn't help with the simple fact that it's completely unrelatable.