Rust and Cargo are, if not inseparable, at least tightly connected. Rust and Rust's stdlib are inseparable.

Cargo is modeled after NPM. It works more or less identically, and makes adding thousands of transient dependencies effortless, just like NPM.

Rust's stdlib is pretty anemic. It's significantly smaller than node's.

These are decisions made by the bodies governing Rust. It has predictable results.