They tried, at least once - I remember when they did - well, can't remember exactly when - think when I was in school but can't recall exactly how old I was - but Americans being Americans we pushed back and said - NOT. You might remember, its when they tried to put the road signs up with both distances trying to "convert" us slowly. Didn't work though so I think they gave it up. (One reason I gather was it was not "mandatory" but "voluntary."
Edited to add: went looking to see "when" we tried to make the Country change to metric - I was right in was in my childhood/school years.
"In 1975, Congress passed the Metric Conversion Act, which declared metric as the preferred system of the United States, and the U.S. Metric Board was created to implement the conversion. . . . (found another article that says that Board was abolished in 1982 by President Regan.)
America began testing road signs in kilometers under President Jimmy Carter,. . ." found in this article (among some others I found: http://www.cnn.com/interactive/2015/07/us/metric-road-american-story/ and this one that explains why we didn't go with Metric way back when in our founding years: http://time.com/3633514/why-wont-america-go-metric/ (several others said the same thing) which says in part:
"The measurement debate actually goes back to our nation’s very beginning. The original metric system was developed in France during its revolution, and was so radically decimal that it divided the day into 10 hours. As our first secretary of state, Thomas Jefferson was charged with deciding which set of measures would be best for the country. He had been instrumental in creating the dollar—the first fully decimal measure any nation ever used. Jefferson rejected the metric system, however, because in origin he found it to be too French. . ."
However, other things in those and other articles noted that many things we buy now list the metric volume or sizes so that we are "partially" there.