For the same reason the metric (literally international standard) system was created. There were many similar systems in use. US Customary was a standard system for the whole country. The problem being solved was different standards for the units. US Customary solves that problem. Only the standard definition of the unit changed. This has been done within the metric system as well, even very recently.

> > Nobody is doing this.

> Yes, people are doing such calculations all the time.

What I mean is that specific conversion with hundredweights.

I’m unclear why anyone would do any of your example calculations in their head. They’re all so important that it would be done precisely on paper or electronically. All a worker pouring a foundation meeds to know is the desired dimensions. All the truck driver needs to know is the quantity ordered. Nobody is actually converting precise quantities of concrete or solar panels in their heads.

You act as if these calculations are simply impossible in customary units, they're not and we do them all the time.

To go on from this, we've converted everything that meaningfully effects our external competitiveness, as I said in a parallel comment I dont think our competitiveness would be helped or harmed if meat was sold in kilograms vs lbs or if we have temperature on the weather forecast in Celsius.

Oh, now you're in US customary unit territory.

Let me introduce you to the acre-foot.

The acre-foot is the unit of measure for reservoirs. For instance, the Ashokan reservoir is 8300 acres with an average depth of 46 feet. Its volume is 381,800 acre-feet.

If an area 10,000 acres received 3 inches of rain, you need 2500 acre-feet of reservoir to put the outflow in.

How big do you need to make your 2500 acre-foot reservoir? Well, if you're working with 100 acres, you make it 25 feet deep.