I can tell you with some (second-hand) authority WHY we didn’t make the switch fully to metric.
10 years ago, I met a gent on a cruise ship who had been big at NASA during the 60s. He was appointed to the commission to address this question. The stumbling block that killed metric was that the union auto mechanics didn’t want to have to buy new tools.
That’s it.
(Also, he said that he heard the challenger audio tape after the explosion, and it was not pleasant).
Yeah. I've always known it existed, and that it wouldn't be for the squeamish.
Fvcking management.