It's notable that the projects you mentioned mostly don't need to deal with adversarial user input, while the projects I mentioned do. That's one area that Rust shines in.
Android team is quite clear that Java, Kotlin, C and C++ are the official languages for app developers.
Chrome even has less Rust than Firefox.
Linux has some baby adoption, and it isn't without drama, even with Microsoft and Google pushing for it.
Chrome only needs to replace the parts of their codebase that handle untrusted input with Rust to get substantial benefits. Like codec parsers. They don't need to rewrite everything, just the parts that need rewriting. The parts that are impossible to get right in C++, to the point where Chrome spins up separate processes to run that code.
Rust is the future for Android, and it will become an important of Chrome and Linux and git (starting 3.0). That's just the way it is.
- Cranelift applies less optimizations in exchange for faster compilation times, because it was developed to compile WASM (wasmtime), but turns out that is good enough for Rust debug builds.
- Cranelift does not support the wide range of platforms (AFAIK just X86_64 and some ARM targets)
There is a whole ecosystem of contributions across the globe and the lingua franca used by those contributors.