The percentage of yield in semiconductor manufacturing is one of the most important indicators directly influencing the volume of production and cost.
The larger the crystal is, the more expensive each defect on the plate. In the case of multi-core processors and other items with multiple similar units can be part of defective crystals to reconfigure the processor with fewer cores. However, because these products cost less than processors in full configuration, to compensate for a smaller percentage of yield due to this technique can only partially.
According to the source, the yield rate of AMD Ryzen very high (probably, this contributes a relatively small area of the crystal). More than 80% of the crystals are working all eight cores, that is, they make the processors in full configuration, bringing in the most profit.