Added ssd disk write and still maintain the original basis

[b6121061]

4t nvme 8 cards are concurrently 1000/m. 8tnvme has 16 disk writes that are still 1000/m. What's the problem?
cpu 5950x
128g
x570
8t nvme Two 2t nvme are on the motherboard, and four 1t nvme are display cards 4x4
8 photos is the best speed. Adding the overall speed will decrease and increasing the ssd is useless, please tell me why

[heus12]

what is X570？

[b6121061]

mainboard