I'm not the author, but the point here is that Apple does a lot to eliminate extra space in its circuit boards. The more space eliminated, the smaller the device can be. Of the three designs shown, Apple has removed the most space. Look how you can barely see traces. Some of this is because it's on a black board, but that's not all of it. Traces are mostly super-short. Google's done a decent job, but has still left extra space in. Traces are fairly long, and there's space between them. Space could have been eliminated.
Now Microsoft? It doesn't give a shit. The underside of the board is half empty. Now, the board can be multiple layers, as seen in a prior image, but that's a lot of wasted space.