Saying its too expensive to change is bullshit. Metric is common enough that most people who care about units at all end up having one set of tools for each system so they can use both as needed. This includes industry and machinists. It wouldn’t actually cost anything to change at this point we could just stop designing new things in imperial units and in a couple decades we would barely need imperial tools anymore, except to work on old stuff. Some engineers are just as pig headed as anyone though, so they just keep using imperial even though they know both, use both, and still run into problems with imperial.