> And again the question why not simply write something new.

There is a ton of new stuff getting written in Rust. But we don't have threads like this on HN when someone announces a new piece of infra written in Rust, only when there's a full or partial rewrite.

Re automotive and other legacy industries, there's heavy process around both safety and security. Performing HARAs and TARAs, assigning threat or safety levels to specific components and functions, deep system analysis, adding redundancy for safety, coding standards like MISRA, etc. You don't get a lot of assurances for "free" based on time-proven code. But in defense there's already a massive push towards memory safe languages to reduce the attack surface.