<igiona[m]> "> <@shakencodes:matrix.org> Is..." <- I have spoken to Steve Klabnik on the same topic. Many Embedded Rust projects use tooling in addition to Cargo: Makefile, xtask, etc. So there are opportunities for enhancements in Cargo when it comes to post-processing of builds.

I attended a session at the RustConf Unconference about building Rust projects. I learned about some of the short-comings of Cargo:
- Using `cc` in `build.rs` is super nice to automatically build C libraries, but cross-compilation does not really work out-of-the-box (you need to tweak environment variables and compilation flags), and some people are concerned about arbitrary code execution during their build (`cc` invokes whatever autotools/CMake build).
- `build.rs` in any dependency can run arbitrary code with no sandboxing.
- Cargo builds are not reproducible.
- crates.io doesn't (didn't) sign packages and is only planning to add TUF
...

People look at Bazel/Buck2 because they have needs/concerns that Cargo does not currently address. Future development in Cargo might make it unnecessary to use those systems. In the meantime they allow people to develop in Rust which I think is the most important bit.
I hope the embedded projects will get larger and larger, because it means they will get cooler.