If you look closely at that image, and at the image of the other side of the board (https://www.jeffgeerling.com/sites/default/files/images/3-pi...), it's fascinating. The keyboard is USB 2 (as mentioned in the article, "one of the USB2.0 ports is dedicated to the keyboard") with its connector is on the right side, and the designer did find a good path from one side of the board to the other, using some crazy routing. It goes between the two USB 3 ports, and then below all the other ports until it reaches the right side, where it passes right next to the antenna and below the wireless chip to reach the keyboard connector. It's a tight fit, and there's no space for another pair.