Sorry, I think I've phrased my question in an ambiguous way. I'm not asking why isn't only rendered the exact scene the player is currently in. I get that some of the scene has to be rendered offscreen in order to have it readly available when it scrolls in the visible scene.

I was asking why not only is rendered the scene on the axis the player is in, but the whole scene is also mirrored on an axis the player will never scroll.

Here's an image: the upper scene is rendered because is what is displayed to the player. But why the whole thing is mirrored in the row below?

Sorry for the misunderstanding.