One of my favourite passages from the Hitchhiker's Guide to the Galaxy is the description of the Shoe Event Horizon. The idea is that as certain economies stall and people start to feel depressed, they start to buy more shoes. This leads to more demand for shoes of differing types, combined with a plummet in quality, leading to everyone having sore feet and buying yet more shoes. This brings about more and more shoe shops, and inevitably society can only produce shoes. And so it collapses. It's a hilarious illustration of the effects of lowest common denominators.
Games, like any business really, are also prone to those same factors. Particularly since behaviourist design returned to prominence (via social games and now gamification) on the promise of metrics, monetisation and new markets, a lot of the same sort of thinking has taken hold. Behaviourists tend to be bottom line thinkers and conservative game designers. They don't care about emergence or unintended dynamics as those things often get in the way. They want their games to be predictable, marketable to the broadest audience possible and fully understandable.
This inevitably leads to bingo, slots, roulette, blackjack, game shows, coupons and bet-driven casual games. In otherwords: extrinsic prize gaming. My thesis is, like the shoes, when a platform starts to become overly filled with these kinds of game it is basically finished.