I don’t believe there’s any special motivation for including Python than what motivates the inclusion of any other of the common Unix tools such as Ruby, Git, grep, or awk.
not to mention ls, gcc, perl, httpd, and the rest of the BSD subsystem on which it is based
It’s been there forever. In fact, Apple used to have semi-official documentation on PyObjC at one point.
A bunch of system utilities are implemented against the version of Python that ships with OS X.
Grep and ask are there for POSIX compatibility, right?
The Calendar and Contacts Server that used to come with macOS Server is written in Python, I can’t think of any system utilities implemented with Python though. And once Python comes with the system (I think it has since at lest 10.4), they can’t remove it without breaking apps that depend on it.
macOS (in its NeXT-based lineage) has always come with many scripting languages (php, perl, python, ruby, applescript, awk, *sh, etc) as part of a standard unixy setup, even before Apple themselves made use of them per se in the system. While they make use of Python currently, it's there also just to enable whatever things a user or a 3rd party may build.