The box shape provides more interior room to hold things, especially if you're spending many days outdoors. The roof is flat so you can put more things on top. Lastly, the shape helps prevent the vehicle from rolling onto the roof like an upside down turtle.

There are downsides however. A box is not aerodynamic so the mileage is poor. At high speeds, the air hitting the box is loud. Mileage is getting regulated by countries for new cars. Comfort is what people are interested in for a daily driving car.