McDonald's uses unique machines that have two hoppers so they can serve both milkshakes and ice cream. More parts, more complexity. They also use a pump inste

McDonald's uses unique machines that have two hoppers so they can serve both milkshakes and ice cream. More parts, more complexity. They also use a pump instead of gravity, so they can serve customers more quickly. That pump is probably what necessitates all these complicated moving parts, and makes it so much more prone to failure.