Thanks for the reminder.  Unfortunately, the macOS installer is working as designed.  As discussed at length in Issue18117 (and elsewhere), building using the -framework Python, either directly in compiler calls or indirectly through Xcode is problematic because python.org Python installers install all versions, 2.x and 3.x, into the same framework location, /Library/Frameworks/Python.framework.  Since it was common especially in the early days of Python 3 to install both Python 2 and Python 3, the decision was made to only have Python 2.x installs add or modify the Current symlink.  As also noted, it was probably a mistake back then to not install Python 3.x versions to a differently-names framework so you can be sure whether you are attempting to link with Python 2 or Python 3 but that ship has sailed.  However now that Python 2 is about to enter end-of-life, we should reconsider that behavior.

In the meantime, there should be a simple workaround: just create the symlink yourself after installing a new Python 3.x version.  So something like:

sudo sh
umask 022
cd /Library/Frameworks/Python.framework/Versions
rm -f Current
ln -s 3.7 Current
exit