There are many computing platforms that rust devs simply cannot be bothered to support (for just one example, Cygwin). The Python devs, by contrast, have actually put in a lot of work over the years to support a plethora of operating systems and architectures.
Requiring Rust as a CPython dependency would be to abandon all their users stuck in obscure environments.
Requiring Rust as a CPython dependency would be to abandon all their users stuck in obscure environments.