From what I've experienced, we use the imperial units for the same reason we use degrees over radians: the units allow for common use of integer multiples of simple fractions. For some people, a simple fraction of a relatable unit really is easier to deal with than a base ten decimal, and a lot of labor out there simply doesn't need higher precision.

Of course, once you enter any sort of engineering work, well, simple fractions often won't cut it and it's far, far easier to simply use a decimal number. And then there's no reason not to use metric measurements.