It’s just logical, and observing stuff. Before metric system, everything was sold by the foot. Have a look around buildings a bit.
Most people are comfortable using stuff standing (like ATMs) if it’s about hip high. Most people have legs that are close to 2/3 of their entire height. It means that overall height doesn’t make that much difference for about 90% of full grown humans. It’s why we can pretty much all sit at the same tables etc too. Most cars fit pretty much any driver. My grandma drove a big old tank of a car at 4’10 (maybe I’m being generous). She looked between the steering wheel and dashboard to drive. Very funny, but probs would have been safer in a different car.
