It's such a deep issue with the C and C++ ecosystem that it's probably what will finally lead systems programming to other languages. It wasn't an issue until the Internet, and still isn't an issue if you are linking against binaries, but definitely is a problem now.

Windows shouldn't be treated like a freak, something too outside the norm to support compiling on.

Windows isn't the only other OS out there, plenty of them on IoT, mainframes, game consoles.

Yes, today nix does not run everywhere C is used. So what? More platforms can be supported in the future.

Then it isn't a solution worth spending any time on.

So if not all and every platform is supported from day 1, then “it isn’t a solution worth spending any time on”?

Nix also runs on Darwin and BSD.

Ok a bit better, doesn't change the fact it doesn't run everywhere where there is a C compiler.

Not everyone using C is writing software that turns on all platforms supported by any C compiler?

Not everyone is writing C software to run only on their own laptop.

I'm confused, do we expect end-users to install a language package manager to use software? Nix would only be used wherever the software is built.

Not everyone using C cares about UNIX FOSS clones.