The Rust module system is radically different from C and C++ and other similar languages in the embedded space.
Every build system that has added support for Rust, which aren't many, had to be radically modified to achieve that.
None of these supports the GCC Rust frontend, but all of them support the Rust frontend.
So if you actually wanted to build any >100 LOC Rust project for embedded targets not supported by LLVM, doing it with the Rust frontend is as easy as just running 1 CLI command to pick its GCC backend.
Doing it with the GCC frontend, would require you to either port one of the build systems to support it, or... give the GCC frontend a CLI API that's 100% compatible with the Rust frontend.
Moreover, modules are less interesting to me in embedded development, for which I'm interested in access to Rust's borrow checker for gaining certainty of small portions of larger projects, which are written in other languages.
Every build system that has added support for Rust, which aren't many, had to be radically modified to achieve that.
None of these supports the GCC Rust frontend, but all of them support the Rust frontend.
So if you actually wanted to build any >100 LOC Rust project for embedded targets not supported by LLVM, doing it with the Rust frontend is as easy as just running 1 CLI command to pick its GCC backend.
Doing it with the GCC frontend, would require you to either port one of the build systems to support it, or... give the GCC frontend a CLI API that's 100% compatible with the Rust frontend.