We don't try to find out what that terrible despair is right away. I doubt that we could succeed in a fast way if we did. But even trying in a focused concentrated way can be too threatening. The person might not be able to bear so much pain. When a person feels more pain than they can bear they may choose self destructive behavior even more harsh than their eating disorder.
Suicide can look like the only option to a person in total despair.
The eating disorder helps the people to not feel their despair. So the work proceeds gently. As people become stronger and more aware, they develop an earned confidence in themselves. They are capable of accepting more realistic knowledge of the world and the kinds of people in it. They then can develop and use more tools for functioning well in the world.