Try this out: Take any current MacOS release, any recent one you like. Now, look at the versions of all the core tools. Stuff like readlink(1). Basic UNIX tools. Look at the manual page, and note the dates. This is the date of the tool it was last synced from FreeBSD.

Spoiler: 10.6 is the last release anything significant in the base system was updated. It's been left to stagnate ever since. For anyone relying on MacOS as a UNIX system for development, testing or heaven forbid, deployment, this release marked the end of any serious maintenance work and the divergence of MacOS X from the mainstream. It's now a decade out of date.

That's not to say no development has taken place. There's a lot gone on at a higher level. But the base system is so outdated it's now presenting real compatibility problems. Scripts which work on Linux and the BSDs may no longer work on MacOS: it's missing a decade of improvements, options, and bugfixes we all take for granted. The complete lack of care here is beyond ridicule. Surely a company like Apple could hire one person to take care of this. It's not like routine maintenance is particularly onerous.