Because no one contributed them

I guess it is pretty easy though, and people have done it before (bitcoin.pro contains MacOSX rules), just install the MacOSX Qt SDK, and build the project using qmake or in Qt Creator.

You need the same dependencies as for normal bitcoin except Wx (follow the steps in doc/build-osx.txt to install them).

I cannot give exact instructions as I have zero pieces of Apple hardware (well except for a dinky first-generation iPod )