Let’s be clear here. Pip doesn’t prevent anything, because pip by design downloads and runs arbitrary code from the internet (that’s what an install from source of a setuptools-based project does). Pip has mechanisms that people can use to limit exposure, but none of them are mandatory, and I don’t expect them to ever be mandatory.
Pip is a component in an ecosystem. And the ecosystem is not designed to be end-to-end secure and curated - it’s designed to promote easy sharing of code, in the spirit of open source. And I, for one, hope that if the goals of more security and code sharing ever come into conflict, code sharing will win - people who need security and auditability have the means to pay for it, and should be encouraged to do so. Python is a product of the open source culture, and should by default support that culture, IMO.