Why can't I run dev dependencies after `pipenv install --dev`?

One answer is that the "dev dependencies" of package X are the packages someone would need if they were developing (as opposed to using) package X.

I would expect that after running pipenv install --dev in my project, ...

If you use pipenv install --dev in your project, pipenv should install all the packages that are required to develop your project.

If it recursively installed all dev dependencies all the way down, it might pull in Python profiling packages, test runners, etc., that other packages need for development. Those wouldn't necessarily be appropriate for someone developing your project.

As an example, if my project listed pytest as a dev dependency , I would be unhappy in pipenv installed nose, which could be listed as an dev depenedency in some other, out-of-date package.

If developers of your package need gunicorn, you should list it explicitly as a dev dependency of your project.