[lights0123]

Python absolutely can run scripts in installation. Before pyproject.toml, arbitrary scripts were the only way to install a package. It's the reason PyPi.org doesn't show a dependency graph, as dependencies are declared in the Turing-complete setup.py.

[oefrha]

Wrong. Wheels were available long before pyproject.toml, and you could instruct pip to only install from wheels. setup.py was needed to build the wheels, but the build step wasn’t a necessary part of installation and could be disabled. In that sense its role is similar to that of pre-publish build step of npm packages, unless wheels aren’t available.