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The fehrenheit scale was developed in the Netherlands around 1724. It was supposed to be the coldest thing they could easily reproduce in a lab (ice salt water) vs. body temperature, but they set body temperature at 96 instead of 100 because being able to divide evenly without decimal points for dividing up scales on his thermometers was important back in the day, and got the measurements a bit off so body temperature is 96.8.

Metric was a product of French nationalism, they wanted to produce their superior man for the future in part by having universal weights and measures and making it based on fresh water rather than salt water. Prior to that, pre-modern France, like the holy Roman empire beside it, was a loosely amalgamated variety of regions with their own laws and customs, which nationalists wanted to standardize. They also standardized language and more. Modernism at work.

So really, it's about two measurement systems made by neighboring countries fairly close together. Since the French revolution occurred after the American revolution, it's just a matter of which European standard they went with, and in a more disconnected world the Americans generally standardized on the older standard that was already the English standard since they weren't immediate neighbors with the Europeans anyway.