So what stops the developers from iterating on a raytraced version of the game during development, and then executing a shadow precalcualtion step once the game

So what stops the developers from iterating on a raytraced version of the game during development, and then executing a shadow precalcualtion step once the game is ready to be shipped? Make it an option to download, like the high resolution texture packs. They are offloading processing power and energy requirements to do so on consumer PCs, and do so in an very inefficient manner