I think the answer to “why” here is (and will always be) familiarity: Rust bears syntactic and semantic resemblance to already popular languages. Ada doesn’t to the same degree.

(This could be framed as a fashion choice, but I think the more neutral framing is precedence: Rust achieves desirable language-level properties without exhausting the novelty budget for people writing non-government software.)

> cite some mission critical software that has been running for a decade written in Rust besides a browser

This will be hard for anyone to do, given that Rust 1.0 was in 2015, so 9 years ago.

However, if you want examples of Rust running in mature, critical environments: my understanding is that Firecracker has been a key part of AWS’s serverless control plane for years now. Similarly, my understanding is that Windows has been shipping Rust in the NT kernel for the last year.