firstly, almost all materials are in imperial. secondly, for construction purposes a base 12 system is mucho easier. you want a 1" and 3/16ths of something? then it's damned easy to measure out. you don't care to be wasting time trying to figure out what 1.1875 is. And you can't say that 'well you'd just use 1.2'. no you wouldn't. the natural progression of measurements in a human is to cut things in halves. symmetry is key to our mind. you cut something in half you get 1/2, then again 1/4, 1/8, 1/16 etc etc. it's jsut how our mind works best. especially in trades where visual is key, it's easier to cut something visually in half, then in half twice more than to estimate 0.125 with you eyes. also base 12 is much more dividable. you don;t need crazy fractions to get 1/3's for instance.