Why should graphics card manufacturers think about making graphics cards for PCIe x8 slots? x16 is the standard that PCs - and especially gaming boards - use. Why complicate things by adding another socket size?
And why do you want to put a graphics card in an Intel Server System? Thats like asking why they don't put a trailer hitch or heavy duty utility wench on a Ford Prius. Its not made to do many of the things expected of a sport utility vehicle.