Half of our houses were built 50 years ago. Even if we had a 'tough but fair' autocrat simply declaring we're moving all newly-installed everything to metric standards, we're going to have to have both kinds of pipes on the truck for 50 more years. That's 2x the inventory to manage for every trade that works on any kind of construction or servicing of equipment.

We can still do a better job teaching metric to kids, without needing to tear down every building to replace all the 2-by-4s with "50x100s." But yeah, that means dealing with the fact we don't have everything following the standards and our pipe threads, screws, etc. will always be different to yours.