understanding why there is no setup.py uninstall

[c.buhtz at posteo.jp]

This question is not technical.
I know that there is no 'uninstall' Option in a setup.py.
I know this discussions and workarounds for that problem, too.
<http://stackoverflow.com/questions/1550226/python-setup-py-uninstall>

I want to understand the design concept behind it.

Why isn't there no uninstall routine implemented?

For me as a user and admin it feels quite dirty when installing
something with the setup.py but then not being able to remove it clean
like I would do it with packages of my system-package-manager (e.g. with
apt-get on a debianized system).