Mesh is what we can look to when we don't have (reliable) Internet, for when we're in places that don't have Internet, and/or for people who don't have the resources to get on the Internet. Rust is not something we're going to be running on low power Pi-type boards in trees, or on the kind of hardware that's available to people with very limited resources. So why write software in a language that isn't meant for and…
Rust is something you don't want to compile on a low-power device. But it's totally something that will happily cross-compile for a low-power device. Many people use Rust for such reasons as high-performance code and low resource footprint of it.
Frankly, you won't run GCC on an MCU either.
But if all you have is an RPi, you can still run the Rust toolchain right on it, if a bit slowly; e.g. https://opensource.com/article/19/3/physical-computing-rust-...