They are in the Windows 8 phase of design. They want to merge mouse and keyboard systems with touch systems, and are thusly forcing mouse and keyboard users to use interface conventions that are derived from touch platforms.
Mobile platforms benefit more from high contrast, very simple and flat designs.
Beyond just the touch screen convenience features -- A significant portion of users is seeig their UI under conditions of extreme sunlight, water droplets, or cracked screen at any given time. These things all inform design choices for mobile.
Now then, why is Apple making the same mistake as Microsoft Windows 8 by forcing these design elements onto Desktop and Laptop market segments? Apple doesn't really think of the PC market much. According to their financial reports, they make more money selling chargers for their mobile devices than they do on the entire PC market.
The answer, I assume, is apathy.