Not all programs use the gpu at all. Many background processes will only use the cpu. They have no visuals or no work a gpu can do and many just idle so don't do anything but take ram. A gpu can't do everything a cpu can. There's a reason they are separate components. Typically the gpu is doing next to nothing in every task except gaming or content creation. Just look at gpu usage. There's a reason why many pcs only need weak igpus. Encoding software that are gpu accelerated typically let you choose gpu. You can have multiple gpus to a single program too. More cores is not the same thing as more gpus. This would be adding cpus not cores.