Rust's standard library is intentionally kept small since it's initially not always obvious what the best solution is and the stability guarantee makes it the w

Rust's standard library is intentionally kept small since it's initially not always obvious what the best solution is and the stability guarantee makes it the wrong place for evolving, diverse or opinionated APIs. E.g. the async ecosystem offers you to pick between runtimes of different complexity and tradeoffs. Std only picked up the essential traits that allow other crates to interoperate with each other and the language itself to define async functions.