Or they knew that they were going to have yield issues, and these dies don't even have a GPU in the first place rather than binning them after the fact.
They also layout with some understanding of the yield (yield is almost entirely a function of die area at a given node). So if they decide to just entirely bin off the GPU, and they know this ahead of time enough, it makes more sense to not have a GPU in the first place. The GPU is about half the die area, so you would get better yield by just not having it at all (but all of this depends on having enough lead time to decide this before layout).