Ground clearance and low wheel size is another big thing with chained systems.
With a gear drive, you want as few gears as possible or else your weight and efficiency really starts to add up. To accomplish this, you'll need big gears (several inches in diameter), which brings the gears rather low to the ground unless you also use very large wheels (8" or more). Here's a diagram of team 25's drive (probably similar to 103's):
The design works because of the very large wheels to accompany the large gears. While great for climbing, large wheels inherently weigh more than small ones and combined with the multiple gears and drive shafts adds to the weight considerably.
With a sprocket drive, you can run relatively small sprockets on relatively smaller wheels.
Here the sprockets for 6 inch wheels are only about 2.5 inches in diameter. This keeps the chain clear of the floor while reducing sprocket weight. The 6 inch wheels in turn are much smaller, lowering weight further.