Rust is not good for raw performance. Neither for prototyping and iteration.
Personally I think operating systems (kernels) should be as performant as possible, and C/C++ has been good enough for decades.
Anyone really unhappy with Linux/BSD/Windows/macOS performance?
What systems are we talking about that benefits from Rust? Advanced weapon systems that should absolutely not fail? Controllers for air planes? Traffic controllers? Radar? Power grid?
Google, fb, amazon, etc. use C/C++ to squeeze the most performance out of anything I/O heavy, and security is not an issue that deep in the stack, that's not the exploitation layer.