Basically, I was at a convention when someone showed a graph of the number of gamers playing games requiring high-end hardware and how it changed over the years. When high-end GPUs started to become common and constantly improved, the number was going up accordingly. But then around the same time of the release of facebook, farmville, etc - There was a huge drop, almost to the same numbers from before the high-end hardware became common. Since then, those numbers haven't changed much, even though the improvement in hardware never slowed down. Mobile platforms (aka iphone/android games) aren't really helping the hardcore games either.
Basically, hardcore games such as GB (or ArmA, or even Starcraft if you only count those who play the competitive mode) are a niche genre on a niche gaming platform... This isn't even mentioning anything about PC vs consoles - For the sake of this post they both count as capable of running "games requiring high-end hardware".