Future gaming and processors

Hello humble people from TekSyndicate. I was just wondering how games affect the Cpu generally and why newer games stress on it more than usual. Today's games mostly work with the videocard of a PC and the processor does only calculations and such. But as seen recently the new wave of next-gen games have pretty high requirements for processing power and I was questioning myself why ?

As people demand more immersive games AIs have become more complex which draw on the cpu opposed to the gpu that's why you used to get away with having a cost cut cpu and high end gpu because there wasn't that much going on in the background.