Python's story for package development is a mess compared to Julia. If you know what you're doing you can make a new Julia package in the general registry with unit tests, CI, and code coverage in about 30 minutes.

To contribute to an existing repository, you can ]dev the package to download the git repository, @edit a function to open the source in an editor, and push the changes to a PR in about 10 minutes. This makes it much easier for package users to turn into package developers.

I've contributed to a bunch of Julia libraries that if I still used python, I wouldn't have contributed to the equivalent python library because contributing to Julia packages is at least an order of magnitude easier.

I imagine it has to do with the fact that lots of python libraries are mostly c/c++ or fortran, while Julia packages are usually just Julia.