Because they're not. "OS X's core is a POSIX compliant operating system (OS) built on top of the XNU kernel, with standard Unix facilities available from the c

Because they're not. "OS X's core is a POSIX compliant operating system (OS) built on top of the XNU kernel, with standard Unix facilities available from the command line interface. Apple has released this family of software as a free and open source operating system named Darwin. On top of Darwin, Apple layered a number of components, including the Aqua interface and the Finder, to complete the GUI-based operating system which is OS X.[32]" - "OS X", Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Mac_OS_X https://en.wikipedia.org/wiki/Mac_OS_X