Do you realize how much testing must go in to checking that all possible combinations of patches work correctly together? This is clearly just cutting the costs of supporting older systems. Now there are no combinations, since each patch gets Windows to the same state, so they only have to test one thing a month. This also means they can test it properly, so you have lower probability that installing a patch breaks your system, which means lower support costs as well.
This is consistent with their effort to move everyone to the latest Windows version, so they don't have to support Windows 7 for 15 years like they had to with Windows XP. They have clearly checked their accounting and found how much money is being spent because of the complicated way they support old versions, and now they are decreasing those costs.
Also, this is the exact same way most other companies release updates. You don't see Adobe giving you the option of selecting which individual DLLs you want to patch in Photoshop. Microsoft is just moving towards the same patching plan other companies already use.
Sometimes I wonder if any Slashdot readers work in actual software companies. Because if you have real world experience with software development, you understand why this is done.
(I am not assiciated with Microsoft in any way)