>and then people simply installed the actual, full version of Python they wanted.
Which then wouldn't work for all the repository python programs. The repo's python is what everything is built and tested against, so there is no replacing that.
The package manager could install its own version of Python, isolated from the rest of the system, so that it doesn't get in the way of the user, but repository programs know where it is and can use it.
Which then wouldn't work for all the repository python programs. The repo's python is what everything is built and tested against, so there is no replacing that.