Because it takes away choices
Right, which forces developers to build MS's tablet app ecosystem for them. And you're right, they are fucking over businesses. But are businesses going to stop buying MS software and support? Not likely. Maybe the next version of Windows will come quickly and offer the option to allow you to boot to a traditional desktops. MS will still get their upgrade money, and they will still have their tablet app ecosystem. Or maybe once enough tablet-capable apps are built, MS will release a service pack that enables this. 3rd parties can even step in and offer stop-gap solutions. So where do they lose?
You're arguing that users are going to lose out in this, and you're right. But what are they going to do about it? Nothing. So again, I ask, why shouldn't MS do this? If you were to walk into a board meeting, what would you tell them that would actually make them agree with you?
I have hardly ever known a mathematician who was capable of reasoning. -- Plato