That would make it difficult to tell at a system level what the exact installed dependencies of a program are. It would also require the distro to basically re-

That would make it difficult to tell at a system level what the exact installed dependencies of a program are. It would also require the distro to basically re-invent pip. Want to invoke one venv program from another one? Well, good luck figuring out conflicts in their environments which can be incompatible from the time they are installed. Now you're talking about a wrapper for each program just to load the right settings. This is not even an exhaustive list of all possible complications that are solved by having one global set of packages.