The UK has struggled to switch from the English system to the metric system. The US began as a break away British colony. Why would we switch when the English have resisted the EU imposed order to go metric. The list of changes needed include repackaging and labeling almost everything you buy at a grocery store, reconfigure gas stations, hardware store items, and the list goes on. It will take 3 generations to forget the old ways and make such a drastic change.