It's got nothing to do with the government, business, or conspiracies.
It's
cultural. It's part of American culture to think of miles and pounds. Yes, there is such a thing as American culture! We tip waiters, too.
In science and engineering, metric is ubiquitous, even here. I guess some disciplines use Imperial units
also, but I doubt you will find an American engineer of
recent vintage who is confused by SI units or who doesn't prefer them. Those guys who crashed that Mars probe were probably old beards.
Anyway, it's not like we're the only one. When I watch
Top Gear, they often speak of miles and gallons. I don't care what the official stance is, the man on the street in the UK still seems to use a lot of Imperial units.
(For the record, I prefer SI, as I did the sciences in school.)