alt Hacker NewsSame reason Android and Chrome and git and Linux weren't written in Rust when they started. Rust didn't exist. All of these projects integrate Rust now, after being single language projects for the longest time.
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.
Rust presence in Android is minimal, and not officially supported for userspace.
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.