Mostly because PCs are modular on axes that aren’t that useful today but also can’t easily be changed. You can’t have the same memory with the same latency use

Mostly because PCs are modular on axes that aren’t that useful today but also can’t easily be changed. You can’t have the same memory with the same latency used for both CPUs and GPUs because GPUs don’t have DIMM and CPUs do, for example. You also can’t guarantee a fast enough SSD to be able to delay loading assets until they are needed.