A significant amount of systems tooling has migrated from perl to python in modern Linux, RHEL relies heavily on it when you start looking under the covers. The basic python interpreter installation ("stdlib") does not include a few key libraries like Requests (think curl) or YAML parsing; these must be installed as complementary (extra) packages on top.

In the article the author makes note of the TOML parser (basically an enhanced INI file design); if a TOML parser is required to install a library (pyproject.toml instructions), and no TOML parser is in the stdlib, how do you install python3-toml (sic) to provide it? It's a circular dependency, chicken & egg problem caused by removing the legacy Setuptools abilty to install a library using only stdlib functionality.

This is only one example, others exist - the OS detection library (needed to know which flavor of Linux you're on) is external and has similar (but not identical) needs, as the python installation paths are different on RHEL-like systems than Debian-like. This one has solutions for it but the author is pointing out those solutions might break based on the current trajectory of upstream thinking.