Some don't even know they're using Python! Here's some examples: Python's in the Linux Standard Base and bunch of critical Linux stuff is written in Python. Distros gotta package those & their deps into their package database (deb/rpm).
Most distros want nothing to do with the language-specific package manager. They want to manage everything though rpm/deb/portage/whatever and they don't want you fucking around with system packages. Ever got burned by Python included with macOS? Yeah, same deal