Truth vs. fiction
Some of the worst movies ever made about WWII -- in regard to historical accuracy -- are among the most popular with the general population. These are, indeed, created via formula as others have mentioned. The worst of these, in my opinion, are "Pearl Harbor," "Force 10 From Navarone," "The Guns of Navarone," and just about everything starring John Wayne (with the exception of "The Longest Day"). These are nothing but sheer entertainment created by people who like money more than truth. If you want to do some serious research on anything about any war, you most likely won't do it in a movie theater.
There are movies, however, which do a fair job at presenting real stories, usually aside from the characteristics of individual "soldiers" involved in said movies. Among these are "Tora! Tora! Tora!", "Midway," and "A Bridge Too Far."
It still comes down to selling movie tickets and creating a popular product, and there is a huge segment of the population that like war movies no matter what they are about. After all, the first Oscar for best picture went to "Wings," a silent movie about two pilots in WWI. And it had little basis in fact.