I think the reason it pervades is the scope. Even WWI was somewhat confined, and the wars before then, like the Civil War, while brutal, didn't touch all corners of the globe like World War II. It wasn't just the first time nations joined forces, it was the first time a global conflict broke out that quite literally involved everyone. It's hard to find anyone, even today, who isn't only one or two degrees separate from someone who was directly involved.
Plus beating the Nazis created two very distinct superpowers, who basically held all the cards in terms of where the world would go from henceforth.