I have thought about this and while the metric system is great for the power of 10 thing thats about it.
I hate the fact that I have to have more wrenches to cover the same ground in metric. Why do they need to make something in 10, 11,12, 13, 14, and 15 (6 wrenches) when 1/4, 5/16, 1/2 and 9/16 (4 wrenches) covers the same ground.
Plus, I spend a long time in the oil business. Converting all the piping, components and equipment to metric would be a logistical and extremely expensive nightmare. I did a piping system once that used some metric equipment and adapters had to be made up for every attachment point so it could be connected to SAE piping. They could have gotten metric pipe and fittings, but then it would mean adapters everywhere that piping attached to the existing system.
I also build a trailer mounted rock crusher system from metric plans. What fun. Easy enough to convert the measurements, but then where it called out for steel made with metric, I had to use available SAE steel, and everything had to be adjusted to keep the proper heights and widths.