One of the ways the author illustrates the daunting task ahead of the men is to make the ocean like a character. Each wave is a "menace."
As each salty wall of water approached, it shut all else from the view of the men in the boat, and it was not difficult to imagine that this particular wave was the final outburst of the ocean, the last effort of the grim water. There was a terrible grace in the move of the waves, and they came in silence, save for the snarling of the crests.
It is as if the men are facing a sentient, malevolent (evil) creature. And this creature is the sea, or Nature itself. In the genre of literary Realism, this story is a classic conflict of Man vs. Nature. And in this case, the men are at the mercy of Nature. Nature does not have a mind and therefore does not care what happens to the men. So, when they ask "why" this is happening to them, there is nothing in response.
Increasing the sense of hopelessness, the author shows how all of the men have similar fears. They are united in their fear and in their struggle for their lives. In Part III, the author suggests that the men, in this dire situation, are all raging against the senselessness of Nature:
As for the reflections of the men, there was a great deal of rage in them. Perchance they might be formulated thus: “If I am going to be drowned—if I am going to be drowned—if I am going to be drowned, why, in the name of the seven mad gods who rule the sea, was I allowed to come thus far and contemplate sand and trees?
The author means to say that the men are so pessimistically frustrated that they are asking why "Nature" would do this to them, especially after so much effort to survive. They are so distraught that they (silently) ask why Nature would do this to them, knowing that Nature will provide no answers. Asking questions knowing there will be no answers illustrates the hope and futility of the situation in the boat.
The author also uses redundancy and repetition to show how futile their efforts are. They work and work to save their lives, but it seems meaningless against the unsympathetic, powerful sea:
In the meantime the oiler and the correspondent rowed. And also they rowed.
The rowing serves a purpose but if the sea "wants" to capsize the boat, it will. The men are facing a foe (Nature/Sea) that is indifferent to what happens to them. Their only hope is that someone on shore will see them and be able to help. Nature doesn't care one bit.