Part of what 3D artists do in games is to create a world which looks great within the engine and the chosen style. Sometimes, often, the style is realism. The Witness is aiming for a different look:

So we began an exploration of different techniques we could use to achieve a sort of stylized realism. We needed to be able to capture the essence of our reference imagery while not being quite so literal. It also had to be free of gratuitous visual noise, plus appealing to look at and explore.

I guess great artists do this consciously or unconsciously. It’s interesting to see it written about. I can’t wait to see the final game.

Eric Anderson’s On the Rocks