American cars have had mph /kph speedometers since maybe the seventies. Only really used if you drive into Canada or Mexico.

I have worked on projects in different countries and the ability to work in different units is more than just being able to make conversions. For instance, you may start with basic manufacturing stock of 0.500 inch (12.7 mm) if designing or making something in the US. But in the metric countries, that is not their standard, so you start out with 13mm. It doesn't make sense to go to the next SI size up and machine down to 13mm in US. So until the basic manufacturing processes are changed to "hard Metric", the products we design and the tools we use will seem to follow the basic manufacturing building blocks. It would be great for everyone to be on the same measurements – and the trend is toward metric. The decimal inch does everything pretty well, that is why it has not gone away yet. The liquid measurements we have (other than ounces) is a real mess, and would be good riddance.