Like you said, Andrew's Desire is to get back home safely every night to his son, and he wishes the same for the other men he works with. The "why" in his case then, is because of his more challenging situation. It's because of the dangerous nature of his work.
It may be helpful to think of it in terms of the function of Complexity for the viewer. Complexity makes us root for the Heart, to believe in his Desire, sustaining our connection to him. What if Andrew worked as a receptionist in an office? How would that change how much we believe in, and root for, him to get home safely?