I'm sure there are exceptions, but generally speaking, do scientists ever really end up working on systems?

Anecdotally, I work with a lot of scientists and they only write scripts. When systems are needed, they hand it off to the development team. Anyone can fumble through scripting, but there is a lot more to think about when building systems, and that's probably not something most scientists want to put effort into – for the same reasons they probably don't want to learn Rust.

Realistically, learning Rust is the easiest part of becoming a systems programmer. But there is little incentive to learn any system language if your workload is always scripting in nature. You are going to, rightfully, reach for a scripting language.