Because previous generation graphics didn't include ray/path tracing or DLSS technologies. They had baked in lighting and shaders that required much less compute to generate. Now that it does it requires more computing power that (we assume) Nvidia hasn't been able to solve with improved higher efficient computing power but simply by pushing more power through the card.

It's what Intel has been grappling with, their CPU's are drawing more and more wattage at the top end.