Someone above posted a Wired article you should check out. Basically, McDonald's uses the same machine to make both ice cream cones and milkshakes, meaning it

Someone above posted a Wired article you should check out. Basically, McDonald's uses the same machine to make both ice cream cones and milkshakes, meaning it has 2 hoppers. In addition, it uses a pump instead of gravity, which allows them to serve more ice cream cones per minute but makes it vastly more complicated. I can see how McDonald's would make a strategic choice to lower their time to serve a customer in exchange for a machine that is broken part of the time. They actually track and chastise workers based on taking more than some absurdly short amount of time to serve a customer. It seems like a corporate strategy for them, and this is in line with that.