I guess part of it depends on the teams/people you work with. I agree - that it would be nice in the python world if we all just agreed, "virtualenv + requirements.txt - Done." - Instead, as you noted, the python ecosystem has split into venv, pyenv, pipenv, Poetry, Conda, ....

Where I work - life is simple. You build your project in a virtualenv so it only has the libraries it needs, generate a clean requirements.txt, check it into git with a requirements.txt - everyone can run it, and, because we have day-1 onboarding to teach everyone virtualenv/virtualenvwrapper - the first thing a person does before installing the application is mkvirtualenv.

I see a lot of references to Poetry here - but I've never been able to interest any of our senior developers into looking at it - they are pretty happy with our existing system.

To be honest, I do expect to find a project provided with a pipenv/poetry setup, just like I would expect a haskell codebase to have a cabal/stack setup, and a java codebase to have a maven/gradle setup.

It is true that most recent languages ship with these from day 1, but ecosystems rarely lack this kind of stuff. I mean, even my vim has a package manager nowadays.

As for whether you want to salvage old code that isn't provided with package management, it's up to you. But you would have this kind of problem with any old, unmaintained codebase.