-One reason could be underbaking the cake. Make sure to follow the recommended baking time and use the toothpick test to check for doneness. -Opening the oven door too early or frequently during baking can cause the cake to sink. Avoid opening the door until the cake is nearly done baking. -Using old or expired leavening agents can also result in sinking. Ensure your baking powder or baking soda is fresh and active.