As I recall when the push for Metric conversion in the US was so big, CNC machining was still primarily a thing of the future. Some folks finely wised up & realized virtually every machine tool in the nation, lathes, mills, screw cutting machines etc, etc were all equipped with English lead screwa. Cost of a sudden change-over would have been Un-Real. Most CNC equipment will now cut either Metric or English with equal ease so it likely will re-surface in the future. It was very easy to look at the virtues if one just ignored all the practical aspects of the switch.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra