Why is the Action Potential of a neuron initiated at the Axon Hillock-Initial segment?

The first poion of the axon plus the region of the cell body from which the axon leaves is collectively called an axon hillock or initial segment. Action potential occur when the neuronal membrane is depolarized beyond a critical level or threshold. This threshold is lowest at the junction of the cell body and the axon or axon hillock, as a result initiation of action potential occur at in the axon hillock. Ref: Textbook of Medical Physiology By Guyton and Hall, 10th Edition, Pages 522, 525; Human Physiology From Cells To Systems By Laurelle Sherwood, Page 98