Also see Embedded C++ as used by macOS IO Kit, which thankfully there isn't a Linus at Apple.
Regarding Rust, no_std, doesn't change the npm like dependencies, macro festival (with two ways of doing all kinds of stuff), abstraction party with type driven development, the compile times.
Partly this is because Rust thought about this earlier, and partly it's because of the relationship between C++ and the allocator, having operators for a feature which might not even exist on your target, awkward.
This doesn't mean using C++ for kernels and such is impossible, but anyone with a conservative, risk-averse mindset (like Linus) isn't going to want to touch it.
Rust, on the other hand, was deliberately designed for such uses, starting from a fresh sheet of paper. Giving systems programmers everything they want without any hidden "gotchas" is its whole raison d'être.
My strong impression is that both Apple and Microsoft are moving away from C++ in their core systems.
Whereas C++ tends to make you eat the whole enchilada.