I must be experiencing a real case of the Baader-Meinhof phenomenon. I hadn't noticed this attitude towards Rust until yesterday, and now I've seen it multiple times since then.
Rust is an accomplishment, but it’s also a very complicated language. It has a harsh learning curve and simply put, not all software written will benefit as much from the guarantees Rust provides. For a lot of software that will benefit the most, people are already experimenting with it.
seL4’s approach also seems interesting. It is doing C with proofs, which in theory should be able to offer stronger guarantees than even Rust if done correctly.