This seems almost as bad as system python. I suppose it's fine if you only work on one thing, but as soon as you don't, your dev environment will become chaotic and lots of confusing WFM will happen. E.g. this is why npm has a separate node_modules folder for each project.
This sacrifies time and disk space and hides tech debt under the carpet, I'd rather have a solution like `pip upgrade` that would upgrade all packages and fix the environment, like `pacman -Syu`, but people would have to stop pinning versions and actually maintain their codebases and the dependencies they uses.
Virtual environments is the mechanism by which you do that in a non-silly way. How do you think people cope with a dependency that has a bug introduced in the most recent version?