That's the other part of the problem. The shell is available everywhere. Python needs to be installed. So, if you need shell-related functionality, it is the easiest route to use.

I have not encountered a system yet where Python isn’t installed out of the box.

Windows, possibly. And as for the *nixes, including Macs, what version is installed? The way Python 2 eol was extended and extended and extended just hurt the whole ecosystem.

Windows doesn't have bash preinstalled so I'm not sure why you're bringing that up. On all OSes I've used in the past 3-4 years all of them have been Python3 by default. The specific version is largely irrelevant as I could ask you the same question about which version of bash is running on a given OS (e.g. it's not available on Mac out of the box as the default shell is zsh due to GPLv3).

  > Windows doesn't have bash preinstalled

I meant Python preinstalled.

  > On all OSes I've used in the past 3-4 years all of them have been Python3 by default.

Windows comes with Python preinstalled now?