[SoftTalker]

You could also argue that North America should convert to 50hz 220VAC for electric services, so that one line of products could be sold to the entire world. But the switching costs would be huge and manufacturers generally have no problem making the few changes that are needed to make products for export, or when possible designing their products to accept either standard.

Cutting metric or imperial threads in a pipe fitting is a programming code change in a CNC machine, and maybe using a different cutting tool. Easily done for an order that's going to be exported.

So I don't think manufacturing is a big concern, and not the reason we've stayed with old standards in many cases.