Yeah, they should just define a new command line option (and perhaps a new command that defaults to this behavior, say vpip or vpython or something.) The virtualenvs take some getting use to. I've been using python for over 15 years so it's second nature.
This is exactly what Node/NPM does: "npm instal" creates a new dir, "./node_modules" and installs stuff there, and next "npm" commands will transparently refer to that subdir. This is, in effect, the same thing as a Python's venv! to the point that in my scripts I always name them "python_modules", to give other unfamiliar devs a clue of what it is.
If "pip install" just did this transparently, without introducing the whole concept of venvs to the user, it would be a huge step forward. I cannot imagine how it would suck if NPM didn't make its node_module dir, and instead it forced you to first learn all the idiosyncrasies of module isolation.