Metric has been legally “preferred” in the US since 1975. We just don’t use it.

Also while I was looking up that year I came across this wild factoid:

In 1793, Thomas Jefferson requested artifacts from France that could be used to adopt the metric system in the United States, and Joseph Dombey was sent from France with a standard kilogram. Before reaching the United States, Dombey’s ship was blown off course by a storm and captured by pirates, and he died in captivity on Montserrat.