even after spending a good chunk of the 1970s learning it in school and being promised metric would be the new measurement standard.

And then Reagan showed up just in time to save us from that Commie nonsense: https://en.wikipedia.org/wiki/United_States_Metric_Board

It also didn't help that the Metric Conversion Act defined it as voluntary, and the U.S. Metric Board was essentially toothless from the start.