Well that's obvious. Super, super obvious. Computer graphics cards are being re-designed and improved every single year.
A console manufacturer can't afford to release a new model of console every single year and rejigger their entire manufacturing process.
If consumers were willing to plonk down hundreds every year for a new upgrade, like people do with smart phones, then sure, manufacturers probably could release an upgrade every year.... but people don't do that. Specifically, kids don't do that. While consoles are brought by people of all ages, a significant portion of buyers are young kids who depend on their parents to buy them a console. Parents are not going to be happy spending a couple hundred bucks every year on an upgraded console.
Consoles are still fine for games. I have consoles, and I'm planning on getting a PS4, an Xbox One and a WiiU (eventually...). I also have a good gaming PC which I upgrade every two or so years. I like all my gaming options.
Consoles are never again going to equal the performance of PCs, unless something drastic occurs in the field of technology. But that's fine. As long as they are good enough, what does it matter? You don't need to drive the fastest sports car to have a good time driving. You don't need to own the biggest house in the world to have a good home life. You don't need "the best" graphics to really enjoy games. My favorite games are "To the Moon", "Bastion", "Final Fantasy IX", "Mass Effect 2" and "Persona 4". Only one of those games requires any sort of graphical horsepower.