It was way too easy for the venv to be the only artifact of the process used to produce it. pip install, hit a bug, install some other dep, another bug, oh this one needs to be downgraded, and so on until it works. Without more effort to memorialize / remember the steps, deleting the venv destroyed the work to create it.

uv, in addition to its raw speed, is very clever to record things in pyproject as the user interacts with it.