Write an essay proposing answers to this question. At the end of your essay, explain how war stories like Where Have You Gone, Charming Billy affect you.
It could be because the situations described in War are so essential to our survival. For many years (I was young for most of them :)), war was portrayed as a kind of "adventure" ---especially since the war movies that I saw always had us "winning" --- if you can win after losting hundreds of thousands of lives. My grandfather was in WW I, and it's interesting that he, as well as many soldiers from WW II and Vietnam, never talk about their experiences. My grandfather was gassed, and the quality of his life was never what it might have been, although he was "cured" and lived until 1970.
Many of the works that have been written since present a much less romanticized view of war. Remarque's "All Quiet on the Western Front" is a must read for anyone interested in a more realistic view of WW I and it's influence on young men. Tim O'brien's books such as "The Things They Carried" do the same for the Vietnam war. Another newer book, "The Book Thief" presents a vision of the "side effects" of war on ordinary Germans in a small town somewhere in Germany.
As I suggested, we need to come to grips with the reality of war because entering or supporting one without a clear vision of what it takes from our young people who wind up fighting and dying in them is a horrible mistake. I would suggest you read all three of these books if you have time.
You almost might want to visit youtube and look up "trench warfare" --- some of the images are an education in themselves.
War is a major subject because it is such a high stress event. Authors like to use the stress of war to bring out the personalities of their characters and to make points about what human nature is like.
I think many people like to watch these movies and read these stories (men especially) because it lets them vicariously experience this experience that is so "manly." They want to feel as if they, too, were risking their lives the way men are supposed to.