Rust developers seems to assume that the only compilation target is x86 or ARM with POSIX API or Windows, or less often whatever architecture is supported by LL

Rust developers seems to assume that the only compilation target is x86 or ARM with POSIX API or Windows, or less often whatever architecture is supported by LLVM. And the rest? There are a ton of architectures that are not ARM, one example is the popular chip ESP32 that uses a proprietary architecture called Xtensa. Another thing is ABI, even if something is ARM, it doesn't mean that its build process is straight forward and you can just compile with LLVM and it works. Try to integrate the SDK of some microcontrollers based on proprietary compilers like IAR, Keil, etc. It's not trivial. Possible in the end, if you want to rewrite all the linker scripts and make sure to build the executable file in the same way, just not practical. Then there are 8 bit microcontrollers, and yes you can buy an ESP32 for a ridiculous price, but what if you need to do something low power? C is universal. Nowadays you can assume that everything that has some sort of processor has a C compiler. With Rust is not like that, and probably never will, since the language is too complex to implement on low cost/low power hardware, and too high level for things that needs a low level access to the hardware.