The rest of the world wonders why the US doesn't use the metric system of measurement. The easy answer is our resistance to change, but that's not the entire picture. There have been various plans to change America over to metric since we broke away from the British Empire. In 1793, French scientist Joseph Dombey set out on a mission to discuss metric measurements with Thomas Jefferson. He never made it, which set the tone for conversion schemes ever since, including the 1975 Metric Conversion Act.
Nevertheless, contrary to popular belief, in the decades since, the United States actually has largely switched to the metric system, just the general public (both domestic and international) seem largely ignorant of this. The U.S. military almost exclusively uses the metric system. Since the early 1990s, the Federal government has largely been converted, and the majority of big businesses have made the switch in one form or another wherever possible. In fact, with the passage of the Metric Conversion Act of 1988, the metric system became the “preferred system of weights and measures for United States trade and commerce”.
In the medical field and pharmaceuticals. the metric system is also used almost exclusively. In fact, since the Mendenhall Order of 1893, even the units of measure used by the layperson in the U.S., the yard, foot, inch, and pound, have all been officially defined by the meter and kilogram.
Schoolchildren learn more about the metric system than ever before, and even change-resistant folks know what a 5K run, a 2-liter bottle, or a gram of weed is. Read the history of the metric system in the United States at Today I Found Out.
(Image credit: Scott Brody)
I disagree that carpentry is easier in English units but I think the biggest problem of modern US carpentry is that even in English units, the actual dimension is different. For example, a 2 by 4 isn't 2 inches by 4 inches. It's actually 1-1/2 inch by 3-1/2 inch.
Why change when when there is no reason?
I am adept in dual units myself - it is like learning another language - and I have no problem. But Americans have been so dumbed down by a failed education system that a major change such as metrification is just not going to be possible even if it carries no cost.