Two different principles. A game engine maps textures to polygons, plus a few optimised post effects. A lot of the detail is already baked into the textures - shading to mimic complex lighting or material properties - meaning you can minimise the processing needed to get the same effect as if it were being calculated on the fly. But what you can do with those textures and models is then very limited.
Whereas in an app like C4D you're producing those lighting and material effects through the genuine calculation of mathematical properties. Some, like blurry reflection, sub-surface scattering, ambient occlusion and global illumination are very complex processes that are nowhere near real-time.
Having said that, you could set up a scene in C4D with optimised textures and no lights, and get something close to what a game engine does. A game engine will still be faster, though, since it's fine-tuned to eek every last ounce of performance form the hardware, whereas C4D needs to be more stable and more compatible.