I don't think CPython needs to bundle all of its build-time dependencies. That principle doesn't really apply to other Python programs nor most other programs in general. AFAIK, CPython already has a build-time dependency on another, external, Python, so it wouldn't be too much to require the external Python to have setuptools installed with something like pyproject.toml (other programming languages usually bootstrap themselves with previous versions of the language along with some associated build tools).