[CarlRJ]

macOS (neé OS X) is actually more Unix than Linux, as it is certified.

[dfox]

That certainly says more about the certification process than about unix-ness of macOS ;)

On the other hand large fraction of UNIX(TM) certified OSes are in fact niche Linux distributions (IIRC mostly RHEL derivates).

In all it is mostly about nobody giving a damn about the certification outside of very specialized applications.