The main issue here is that they don't want the hassle and responsibility of breaking everyone's software each time they release a new system-level python.
They have a problem deprecating python2.7 as it is, the smartest deprecation is not to release a python3+ version at all.
You see a similar issue with python on Debian. Python 2.7 is still the system python for all of the Debian tree, and it is very challenging to migrate to a new version because of the huge impact it has.
That's not to say MacOS won't be a place where python is happy to run - just that Apple don't want to dictate a specific version of it in their releases (i.e. developers/users/applications should install one.)
They have a problem deprecating python2.7 as it is, the smartest deprecation is not to release a python3+ version at all.
You see a similar issue with python on Debian. Python 2.7 is still the system python for all of the Debian tree, and it is very challenging to migrate to a new version because of the huge impact it has.
That's not to say MacOS won't be a place where python is happy to run - just that Apple don't want to dictate a specific version of it in their releases (i.e. developers/users/applications should install one.)