"Many people have asked us why we didn’t build a four-wheeled cart that wouldn’t need to be balanced. However, four wheels would double the rolling resistance and thus the effort required to push the cart. Furthermore, a four-wheeled cart is less maneuverable and more difficult to drive on uneven terrain. You also need to get two extra wheels, and you need to build a steering mechanism. "

I would have asked them why they didn't make a 3 wheeled version. Keep the two big wheels on the side, add a smaller freely rotating one in the front, like a lot of strollers have. They could make it just a tiny bit too low, so it's easy to roll it with both 2 or 3 wheels.