I don't genuinely understand what's wrong with setup.py and why people wouldn't just use setuptools, as it is even suggested by PyPA.

IMHO Python should improve what it already has instead of pushing the usage of third party tools for a core component such as packaging.

For all my Python projects I just use setuptools and the built-in venv module for isolation.

What I feel it's really missing is an official way to have multiple Python version installed.