The main reason is because sony doesn't have an OS to pitch to pc owners. Sony doesn't benefit if it's first party exclusives went to PC and people would have less reasons to buy a PS4. What MS is doing with the whole cross-buy thing will likely hurt anyone's incentive for buying a xbox one but it will greatly add more value to windows 10. It's obvious which is ultimately more important to MS.
I disagree with the idea that exclusives are becoming less important. They are becoming more important in my opinion. Without a doubt, third party games sell truck loads but exclusives are what makes a console distinctive. Otherwise, there would be no point in owning more than one console because they would all be relatively the same. It's the most logical way for a console to really stand out from the competition other than going with gimmicks.
