The reason time.thread_time() and several other functions in other modules that all depend on features in newer versions of macOS were not available in python.org macOS binaries because the installers are meant to support a range of operating system releases (rather than just one operating system version as with most other distributors) and, up until recently, the only supported way to do that was to build the binaries on the oldest supported system. Thus most python.org installers in recent years were built on macOS 10.9 where time.thread_time() does not exist. As of Python 3.9.1, with the addition of support for macOS 11 and Apple Silicon Macs, support for "weak-linking" was also added meaning that it is now possible to build Python 3.9.1+ on, say, macOS 11 and have it work without crashing on older systems. Currently, we only test back as far as 10.9. This feature is in the 10.9+ "universal2" variants available for 3.9.1+ releases and for 3.10 pre-releases.

https://docs.python.org/3/whatsnew/3.9.html#notable-changes-in-python-3-9-1