Market segmentation and manufacturing optimization. All client CPUs have the same amount of PCIe lanes (24, usable). I.e. either it’s a 200$ 7600 or 700$ 9950x - all get the same amount. Why? Producing single layout/spec is cheaper than producing many (that would probably need different flavors of IO dies, PCIe IPs, etc). Thus, to make it profitable - here is your segment, a client CPU with 24 lanes. Want more? Here is Threadripper, 88 lanes, but the cheapest is 1500$