Imperative dependency (mis)management. Pip resolves what needs to be installed while it installs things depending on the setup script of the package. It require

Imperative dependency (mis)management. Pip resolves what needs to be installed while it installs things depending on the setup script of the package. It requires a full execution and it is neither repeatable nor reproducible. So it is impossible to know what needs to be pulled from Pypi ahead of time. Pip is also strongly tied to the specific Python version. If you upgraded Python interpreter on a system, congrats all virtual environments and all PyPi packages are broken now. Hopefully you saved the minimum set of requirements and they don't have some catastrophic dependency breakage. You run pip install and pray. What? Native binaries? Building them on the fly while installing a pip package? Oh you're brave.