Dr. Annie McKeown O'Donovan:

The concern that happens when death is not imminent is because of the possibility of life getting better. If someone wants to die with assistance due to chronic mental illness or for other reasons there is the possibility that life might get better for that person. When death is imminent, the period of life that we are concerned with is of a very short duration. Life is going to be over soon anyway. It is about making this short period of time as tolerable and as good for the person as possible and that helps us to narrow the parameters.