In the Windows installer, "Add Python 3.x to PATH" is unchecked by default:

https://docs.python.org/3/_images/win_installer.png

If it's unchecked, then "python", "pip", and any other commands from installed packages (like django-admin, etc) will not work, which is quite important functionality. Searching on Google shows that "'python' is not recognized..." is a commonly asked about error. Many users leave that box unchecked because they don't know what PATH is and they tend to stick with the defaults recommended by the installer.

On the other hand, I think not wanting Python on your PATH is more of an advanced use case. The people who opt for this are more likely to know what PATH is in the first place, so it's reasonable to ask them to decide to uncheck it.