Why? I find myself using metro as a second desktop for shortcuts or quickly typing to find programs, WAY faster than old start menu and its thousand clicks to get where you want
Too many clicks to get between windows and programs. Yes the Metro type search is good, but I search for practically nothing, as I have all of my must have programs on the desktop. Music is in music, pictures in pictures, etc so file wise my structure is simple and fast. Settings are out of the way, in a bad sense. It is harder to manage the PC if you're a power user using Metro, as most of everything is hidden and you only get the "first step" typically within the settings/options of Metro.
On top of that, the desktop file explorer defaults to using Metro UI when you open files, which I find bizarre. Just another way of trying to met Metro down our throats.
There was no need to force it upon users IMO. Desktop/Laptops should have Metro optional and desktop standard, and tablets and touch screen laptops/desktops should have Metro standard and Desktop optional (for non ARM chips). People have interoperability across devices if they need it, luddites keep their old approach, and you still get a fresh take in Windows for newer technology.