probably because their objective has met its goal which is to kill off pc gaming.
Huh? Then how is Blizzard printing truckloads of money without publishing a single console title of any kind? All they have managed to kill off is "Microsoft Games" as a PC gaming brand - the own goal they did with their artificially Vista-exclusive Halo 2 and Shadowrun was so spectacular that no wonder they are hurting.
Blizzard and Valve are both making gobs of cash by playing to the strengths of the PC market. If other companies are too clueless to see what works for the PC and instead keep churning out crap in shiny boxes for the store shelves, they deserve to go bust.
PC also has plenty of new and independent developers all ready to bust in to fill any space that might open up in the PC market as big names move over to consoles. Sure, there's tons of chaff, but it's a tough world out there - survival of the fittest. If you make a good game on a PC, and have any clue as how to market it, you will make money. You just need to adapt to the market.