This was not a "mistake":

      So it's a matter of mathematical and physical fact that to expand
      the address size, you must change the protocol, and that means 
      [three] things immediately:

            You have to change the version number.

            You have to add new code to handle the new version.

      […]

            You need a coexistence technique so that updated systems, 
            with the new protocol, can connect to old systems that know 
            nothing of the new protocol.

      Two minutes of thought show that this third requirement has only 
      two solutions:

            (3A) Dual stack, in which the new machines speak both 
                 the old (IPv4) and new (IPng) protocol.

            (3B) Translation, in which something translates addresses
                 between the old and new protocols.

* https://datatracker.ietf.org/doc/html/rfc1671

Pounds vs kg, similar story as F vs C. Pound is pretty much the human-discernible granularity. Otherwise doesn't matter.

0-100 MPH lines up well with car speeds, which is usually the thing you're measuring with that. KPH is excessively granular for that. Probably not by design, but yeah.

The feet/inches vs meters/cm thing matters less. It's base-12 vs base-10. You can do decimal feet or fractional meters of course, but it's less common, so apparently both ways are fine.

The nice thing about imperial (as well as the customary system used in the US) is that it's based on measurements that people have found useful over thousands of years. They're human units, adapted to what people need to do with them, not the other way around.

It's difficult to explain to metric folks because it's really something you have to experience. But here's an example:

Reservoir volume in the US is measured in acre-inches. An acre is a unit of area used for measuring property, usually farmland. It's a bit less than half of a hectare. And of course an inch is 2.4cm. Acre-inches sounds totally bizarre when you first hear about it. But for the people that need to work with this value, it's an extremely useful way to measure reservoirs and gives you an intuition that you just don't get from cubic meters.

It's true that you can't just convert that to other units of volume without doing some math or looking up the conversion rate, but that rarely matters. If you're trying to figure out how fast the lake will rise or fall with a given inflow and outflow, you're going to have to have some way to account for the fact that the lake is a) an irregular shape and b) takes up more area the higher the water gets. You already need to know the area of the lake at any particular height to work out the evaporation rate anyway, so that's a number you're going to have. The units are designed to make that calculation easier, which was really important back in the days when slide rules were the state of the art.

All the customary units are like this in one way or another. They're units designed for a particular domain, and when used in their domain they work very well and calculations can be done in your head. They use fractions because that's what people have historically used (seriously - my grandfather could work fractions in his head faster than I could type them into a calculator, and he made asphalt for a living. Imagine what a carpenter could do.).

Think about it. Imagine you were never taught a measurement system. You find yourself needing to come up with a unit to make measurements for wooden planks you're going to use to build a house. Would you choose a unit as long as a meter? Or one as short as a centimeter or even a decimeter?

Bonus challenge to the fine folks clicking that downvote button: give me a real practical reason to prefer Celsius to Fahrenheit, besides the fact that Celsius is part of the metric system. No, the freezing and boiling points of water don't cut it - I work with hydrocarbon fuels, I salt my driveway and patio, I don't live at sea level, and quite honestly every American 8-year-old can spout off 32° and 212°. There's a Fahrenheit equivalent to Kelvin (Rankine) so the Kelvin to Celsius equivalence doesn't count either. My claim is that both scales are completely arbitrary, and only advantage one has over the other is that you're used to one of them. Go ahead, prove me wrong!