Once you start binging/purging, why is it so hard to stop?

In one way, it is habitual and, we all know it's hard to break habits. However, binging/purging is a way to let go of emotions, to feel some sort of relief. It is a coping mechanism and, when something like binging/purging becomes a coping mechanism, it's hard to stop.

In my opinion, it’s because it is very difficult to get rid of / reduce the guilt one attaches with eating food. Not being able to refrain from eating, to a person suffering from an eating disorder (most likely bulimia), generally will lead them to think that they’ve let themselves down, and that if they don’t vomit/purge, they’ll have to somehow learn to bear that intense guilt. Sadly, for someone undergoing an eating disorder, vomiting seems like an easier choice as not only will they think that the guilt will be over, they’ll also feel relieved that they’ve managed to satisfy their taste buds, but also managed to prevent the food from fuelling the body. In summary, it’s because one believes the guilt will never be over unless they purge out everything before it is fully digested by the body.