Why does the sailor help David jump ship instead of reporting David to the captain

The sailor helps David jump ship instead of reporting him to the captain because he feels sympathy for David. The sailor recognises David’s desperation and innocence, and although reporting him would be the “proper” thing to do, his compassion outweighs his duty. He understands that David is seeking freedom and a new life, and by helping him escape quietly, he gives David a chance at survival rather than subjecting him to harsh punishment.