About many games you can say "oh that's the Unreal engine for sure", "this was made by upgrading GTA 4", etc. We can often recognize the engine used for a game just by looking at its graphics (disregarding menus and such).

I'm wondering, why is this? All game engines use the same 3D rendering technology that we all use, and the different games usually have a distinct art style, so what's left to recognize?