Actually, I think while there could be a wide range of factors behind the problems, there are three big ones:
1) The rise in development costs. Watch the credits for a game released in the last year or two. Compare them with the credits for a PS2 era game. Then with an even older game. There are a lot more names there these days. If you want to look at all competitive in the mainstream commercial market, you have to invest a hell of a lot in development. I remember when Wing Commander 3 was launched, people cooed over its $4 million budget (a lot of which had gone on paying its acting cast). Â£4 million doesn't buy you much in games development terms today.
2) Prices have fallen in real terms. When my parents moved house a couple of years ago, I cleared out a load of my old stuff from their attic, including a load of 90s video games - many of which still had their price tags on. Games like X-Wing and Gunship 2000 - for the PC, not consoles (so no licence fee to be factored into the price) - were sold for 45GBP. You wouldn't pay that for a PC game even in a high street store these days. On Steam, you very rarely pay beyond 30GBP even for a brand new title. Factor in inflation and that's a huge real-terms price cut for the average game.
Now, those two themselves wouldn't be fatal - they were true to an extent during the PS2 era. But there's a third aggravating factor now:
3) The market isn't growing at the speed it once was. From the launch of the original Playstation through to around 2008 or so, the gamer demographic went through a massive expansion, breaking comprehensively out of the kids-and-nerds niche (and expanding within that niche as well). That expansion hasn't quite stopped now, but it has slowed considerably. For a moment it looked as though the original Wii might pressage a further quantum shift in the size of the gaming demographic, but instead the tide rolled back a bit - many of the non-gamers who bought a Wii reverted to being non-gamers after a couple of weeks.
This slowing in the rate of expansion is probably due to the economy to an extent, but also due to the fact that the low hanging fruit - the people with the capacity to enjoy gaming - has already been largely picked.
Having development costs soaring, prices at the till falling and the market's growth slowing is a recipie for disaster.