[dragonwriter]

> the shell script is just for convenient of inserting the bin directory into the $PATH so just "python" or "pip" runs the right thing.

Or so any reference in the program you run that launches another binary or loads a DLL relying onnthe environment gets the right one, etc. There are some binaries you can run without activating a venv with no problem, and others will crash hard, and others will just subtly do the wrong thing if the conditions are “right” in your normal system environment.

[josephg]

Another implication of this is that its impossible for 2 mutually incompatible copies of the same package to exist in the same environment. If packageA needs numpy 1.20 and packageB needs numpy 1.21, you're stuck.