Because infinite numbers are not a natural expression of discrete measurements, and when it comes to being price 1/3 = 4 is always going to be easier to put your finger on than 1/3 = 3.333.

I work in software and data analysis in the construction industry. A continuous measurement is good for some things, but it's definitely not good for discrete measurements. Furthermore, a lot of the people who work in the field for construction greatly prefer Imperial for a reason. They have no bias towards systems beyond what works fast and easy.