I thought people did Rust, which has some challenges, principally for speed and for low level security. I had no idea that it was used for stable build environment. I am surprised. But if a stable build is wanted what is wrong with, I don't know, Java or maybe python.
Discussion
I program almost exclusively in rust. I like the low-level access, the low-level performance, and the security. Things that compile very often just work the first time. But I've also come to appreciate that things that compile on my machine compile on everybody else's machine too.
However, I dread linking to system libraries and fighting the bugs around version differences. Some things only work in linux... some things work in linux/windows/mac but not in WASM in the browser. And not on riscv machines. But pure-rust works everywhere: WASM, riscv, etc.
In gossip, you can include ffmpeg and have video playing inside the client. But it' a pain to maintain when ffmpeg updates and to maintain it working for all older versions. I had similar issues with OpenSSL. This is because I'm linking to a system library under usually /usr/lib which may not be the right version and may not compile.
RustCrypto is not as fast as ring (rust, but not as portable), or openssl, or boringssl. But it is not at all slow. And I haven't tested the performance. In any case, I could now go off and tweak the boringssl backend to my liking and get higher performance. It's just not what I plan to do next.
Java and Python both have portability issues. Ever build Sparrow or Electrum from source?
Also, from rust I can build interfaces for other languages like python, java, go, javascript, etc.
I started coding in rust in 2014 or something like that, back around version 0.6 (I dabbled around version 0.4) and helped when they were defining the language for 1.0 release.
Rust does have some challenges still. But fewer as time goes on.