[HCIdivision17]

You don't really recalculate that stuff over and over, do you? Every electrician I've worked with has a couple of the main ratings memorized and just applies it to standard. Anything more complex requires a calculator or tables either way, and once you're not doing the math in your head, it really doesn't matter what units you use. They're all arbitrary, so you may as well snap 'em to an integer value of convenience.

You'd certainly also want a universal one for conversion, but not for every day tedium. Fahrenheit is nice because it spans the human experience in a nice range (say damn cold 0 to rather hot 100). But that's bunk if you're in context of chemistry where water's properties are far more comparative (0 freezes to 100 boiling). Though absolute scales are always a bit sporky, since they latch to a scale and wonk it sideways (-273 is a silly number no matter what anyone says).

And so on. Scales and units are merely benchmarks. Literally. Pick the right bench for the job and follow the marks.

(Though with enough effort you can make any scale work. Kinda like hammers and threaded carpenter nails.)

Edited; typing on phones ruins grammar.