In Python, if you're running 3.7.1 then you're also running the standard library for 3.7.1. Sure, I guess it would be possible for a programming language to decouple these things so that it's possible to ask for a particular version of the standard library (in its entirety), or a particular version of a standard library... but then programmers can no longer rely on the standard library to "just work" and "just be there", which is its appeal. If you decouple the standard library from the language, might as well switch to a Rust-like system where you simply give an official stamp of approval to certain packages regardless of who developed them.