So how is using yet another different system defining arbitrary measurements that cannot be easily converted, do not directly correspond with the radix 10 numerical system, and are also not widely used make things better?

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.