They have their place. But the default shouldn't force you into a "project" when you want general purpose applicability. Python should work from the shell as readily as it did 20 years ago. Not mysteriously break what used to work with no low-friction replacement.
Python can work from the shell, if you don’t have external dependencies. But once you have external dependencies, with incompatible potential versions, I just don’t see how you could do this with “one environment”.
A python virtualenv is just a slightly more complicated node_modules. Tools like PDM, Poetry and uv handle them automatically for you to the point where it effectively is the same as npm.
The thing that makes Python different is that it was never designed with any kind of per-project isolation in mind and this is the best way anyone's come up with to hack that behaviour into the language.
The brilliant part about venvs is that A and B can have their completely separate mutually incompatible environments.