celador on 07 February 2014
Lots of different reasons.
Most of the annual games have been going for a long time and people are getting bored of them.
Games like GoW, Metal Gear Rising and Gears were spin offs and were never going to sell as much as the main series.
Sly Cooper is an old IP and a platformer, and aside from Mario those kinds of games never sell as much as they used to.
Some games, like Dead Island Riptide and Crysis 3 don't deserve high sales because they are not very good.
The other games you listed are concerning though, games like Tomb Raider and especially Bioshock deserved to sell more, but there are only so many 'hardcore' gamers around, and clearly not enough to sustain as many AAA titles as are being released.
