To put it simply it's because Windows 8 is for content consumption, not content creation. And it really seems to show in how Microsoft markets Windows 8.
Though I don't suggest that content creation has completely dissappeared, but it seems to be a bit more of a neglected need as a operating system. Sure, you can do a bit of playing around in Fresh Paint, but when you needs to do more serious things like some programming your just dropped into desktop mode in a way which the Metro UI is saying "Duuude, your boring!"
I titled this "Why *I* don't like Windows 8" specifically because to be honest, there's a lot of people are aren't like me. People just need a PC which satisfy their gossip, casual gaming and porn needs, and Windows 8 is pretty damn good at doing that.