Why did the United States never switch to the metric system like every other country?

This question is quite similar to the one about force America to use Celsius, but I am more interested in the country’s history of metric/non-metric usage. It seems like it did use it at one point, like 1821, when it officially defined the US foot as 0.3048 meters, but I am unsure of what exactly happened in the 1970’s that made that go away. So here’s my question: why did the US never fully convert to the metric system?