Because, as the article states, the OS interface is C. In order to do anything useful at all in your code, you need to call through the C API of your operating

Because, as the article states, the OS interface is C. In order to do anything useful at all in your code, you need to call through the C API of your operating system. To replace this, you would need another compiled language. It can't be "any other lang" - it needs to be something compiled down to machine code that can be directly executed on your CPU. So you could write a new OS that presents an interface in Rust, or Zig, but never WASM.