It's a simple matter of interest, really. WWII was, by and large, DRAMATIC. Dunkirk, D-Day, Blitzkrieg, Pearl Harbour and Hiroshima. WWI was mainly categorized by 19-year olds sitting in holes in the ground in Belgium and France, taking pot-shots at each other. The most ominous, familiar event of WWI to most people is the fighting in "The Somme" which, when it all comes down to it, was just thousands of men running up a slight incline and getting shredded by machine-gun fire. Plus the First World War didn't involve Millions of civilians being murdered for their ancestry, and the Second has far, FAR more documented history surrounding it.