This was a conscious decision by Rust folks. Let the language and std libraries be small enough to target anything - and let well-established crates (most writt

This was a conscious decision by Rust folks. Let the language and std libraries be small enough to target anything - and let well-established crates (most written/started by the rust folks) fill in functionality. The main language provided the baseline interfaces, in some cases (see async), but not the machinery (e.g., async runtimes).