>The second appears to be untrue; if you removed the concept of undefined behavior from C, it wouldn't get farther away from the hardware

My understanding is that even common CPU instruction sets can have undefined behavior[1].

When C was written, the CPU architectures were more of a Wild West. It might have made sense to leave some parts up to the compiler authors on a particular architecture.

>Is that first point actually something that somebody wants?

When C was written — absolutely.

Portability of C code is almost taken for granted these days.

Things were different then. Portability was a big challenge.

All that said, this is my non-authoritative understanding of the reasons why it's a thing. Take it with a grain of salt.

>At that point, you've given up on having a standard

Sure. Just treat C as a family of languages which have a common standardized part.

Proprietary compiler extensions are/were common anyway, so that's not an unusual situation.

[1] https://www.os2museum.com/wp/undefined-isnt-unpredictable/