A wild shot in the dark on IW's decision in regard to the PC version, focus on the console market and making big money?
You dish up a console ported PC version, but cut the longevity of the game and community base with no mod support or dedicated servers. Focus on milking the franchise with DLC and give it 6 month's before hyping the spin machine for the next MW sequal in the money train.
With a lack of dedicated servers and support for Mod's you cut the longevity of the game to your PC market, making those that do buy it more interested in buying the next sequel in the series. That's why so many developers who made their name in the PC development market now focus on console gaming development, it's easier to churn out games and sequels in the knowledge that the longevity of games if purely based on cash based DLC rather than community based modding that is a major point of much of the PC gaming scene.
It's a great shame that IW has such a short term memory, it was the PC market and gamers that made you successful in the first place, now you turn on your major game purchaser and give them a clip round the ear, sensible not.