I think it really all comes down to money. PCs are really expensive. Not as expensive as they used to be, but they are still a lot more expensive than consoles. For people to constantly upgrade to PCs that can play the latest games, there needs to be enough really good games out there to entice them. At the same time, the cost of developing games has gotten much much higher. Where a developer previously might have only needed to spend $500k to make a game, now it might cost them in the millions, so a lot of small developers go under or get bought by the likes of EA. As developers go under, less games are made, thus less people upgrade their computers, and thus less people who might have otherwise bought a new game don't because they don't want to invest the money for new computer hardware. Similarly, there is a lot less justifcation for upgrading computers these days for "business" purposes. There isn't much of a reason to buy a $500 video card other than to play videogames with.
I think ultimately the reason you play games less on your PC is because there are a lot less games to choose from now days. That, and there are many more games to choose from on consoles.
Nite_Hawk