Their forefathers were actually in favor of the metric system. The US is an original signatory to the treaty of the meter, it's the official unit of measure for the government and military, and we were on the brink of getting switched over when Republicans decided they didn't want to spend money on the final conversion and education, despite it being a popular enough notion that it was used for advertising. (The two liter bottle became popular when they used the popularity of metric to sell plastic pop bottles).

The fervent attachment to imperial is weirdly recent.