For example, with virtualenv you can choose to use a mix of globally- and locally-installed packages. With venv you can't. (You get global or local, but not both.)
The database driver and scipy are installed globally. Everything else is local to the environment.
Not hell at all, especially compared to compiling numpy/scipy every time you want to spin up a venv that uses a single feature.
Examples other than DB drivers and scipy exist. Compiling software isn't really that hard, but it's an unnecessary hurdle in many cases - especially when you've already bought into an OS that does binary distributions specifically so you don't have to compile anything.
I'd be comfortable agreeing that any pure-python package should be venv only, but not that every package should be.