Back in the fifties many people were convinced that we would convert to the metric system, but one facet that held us back was architecture. The standard wall stud is placed in intervals of 16 inches exactly, making it easy to find studs to hammer into if they are placed correctly, however you convert that to metric and you get 0.4064 meters which can be difficult to measure. The majority of houses and buildings that are in the U.S. have existed for at least five years, it would be impossible to change the stud placements in every structure in America, and if this did not happen, then how would you ever know if your house had studs place on foot based or metric based intervals. This is not a small problem, knowing where the studs are are important in most wall operations more invasive than hanging up a picture frame.
Similar problems were foreseen with other types of infrastructure, such as bridges and road, plus in reference materials like maps.
It's a good idea to change it, but the costs needed to make it happen are way to high to be feasible.