In its inception 35 years ago the creator of python could not foresee how far python would go and how the environment would look like today. But nowadays there are a lot of security mechanisms they could leverage to adapt (from chroot by default to namespaces, cgroup, etc. on Linux, pledge, unveil on OpenBSD).

The very idea that you offer a (python) package installer that is gonna pull a tree of code published and updated by random people in an unvetted manner open the door to all the supply chain attacks we are seeing.

Around the same time (early 90s) Java was designed with high isolation in mind but the goal and vision was very different. And Java had its own problems.

I'm saying that because at some point the security problem is gonna really hurt the python ecosystem.