The GPU was fabbed on a mature 40nm process and they weren't able to reduce costs with a die shrink due to the lack of eDRAM on 28nm. The CPU probably could have been shrunk, but being such a small die in the first place there wouldn't have been much saving. The MCM packaging itself might have come down in cost a bit, but is still an expensive process. The DDR3 was already mature and cheap, so there wouldn't have been many savings there. The same would be true of most of the controller components.