The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units.

Why the US uses the imperial system. Because of the British, of course. When the British Empire colonized North America hundreds of years ago, it brought with it the British Imperial System, which was itself a tangled mess of sub-standardized medieval weights and measurements.

The US Customary system of units was developed and used in the United States after the American Revolution, based on a subset of the English units used in the Thirteen Colonies; it is the predominant system of units in the United States and in U.S. territories (except Puerto Rico and Guam, where the metric system is also officially used and is predominant, which was introduced when both territories were Spanish colonies).

Workers in North America learned the British system of measurement as part of their working lives, but they also used it at home too. That meant buying meat by the pound, milk by the quart and measuring height in feet and inches. Kids grew up learning the imperial system at school.