Re: Why?
Rust has guaranteed backwards compatibility, except for a few small things, so it's "instability" doesn't matter. They also readily provide binary, prebiolt toolchains even for old versions, so you can simply specify that you want whatever version of you absolutely have to.
Rust also does support dynamic linking. There's just very little reason to use it most of the time. Android actually provides some interfaces and such through Rust, and they are shared libraries.
You're really only correct about not having inheritance, and that limits replacing some c++ programs; however, Rust traits can provide some similar functionality with its traits, which is a form of composition. Some of it is down to personal choice and debatable, but many cases of inheritance can be replaced by and better designed with composition.