I believe, it's because various Python libraries ship with a pre-compiled C/C++/Rust library. That library needs to be compiled for a specific target, and you often only get Linux x86_64 on Pypi, because that's what most library devs use themselves.
Conda tries to solve that by providing a separate repository, where they do have builds for more targets available, but as a result, they have fewer libraries available in that repo. That's why we needed to install some via Conda and some via Pipenv/Pypi.