^ If I can try to steel man this, it may be that having two different languages is simply worse than having one, even if the one language is non-optimal. Sure, if you were starting Linux today you wouldn't choose C, and hopefully Linux won't be the last operating system to ever exist, and the next one can use Rust. But Linux uses C, and no one is contemplating a full rewrite, so it's best to stick with C.

I have no idea if this is true, I am very much not a kernel developer.