While CFexpress cards are excellent media with fast read and write speeds, we believe that there is also a need for the SD card as well because they are more readily available and easy to get.
The Z8 is designed to be widely used by high-end amateurs, as well as customers who do not need high-speed continuous shooting, such as landscape and portrait photographers. By using the SD cards they already have, the Z8 is designed to be used in a wide range of shooting applications, so this is a consumer product.
When recording RAW and JPEG at the same time for high-speed continuous shooting, the performance may be degraded if the SD card is a very low-grade one, but there is no significant performance degradation if the customer is using a UHS-II type SD card. So as long as Nikon-recommended cards are used, there will be no significant reduction in performance.