Clearing all of the frosting could be difficult since they're in the top row. There is restricted board space, and the frosting are in the corners.
You also have to clear a lot of liquorice. There are only 52 starting liquorice swirls on the board, so you have to clear 13 more to get the order completed. Also, you have to clear the frosting before you can even spawn any more swirls.
Bombs also come out of the cannons, and at 12 moves, they can be hard to clear.
The orders are worth 12,500 points. Hence, an additional 77,500 points is required to earn one star.