Comment by nine_k

It's a win because they have to test one chip, and don't have to spend resources on connecting the chiplets. The latter costs a lot (though it has other advantages). I suspect that a chiplet-based device with total 900k cores would just be not viable due to the size constraints.

If their routing around the defects is automated enough (given the highly regular structure), it may be a massive economy of efforts on testing and packaging the chip.