When i say poorly depicted, I mean poor in terms of historical accuracy. More specifically, I'm thinking about films such as Ironclad, Kingdom of Heaven, Vikings, that sort of thing. Vikings and Kingdom of Heaven are great, but they're not entirely accurate.
History is not the primary goal of most media. It isn't even the secondary goal. History is, for the entertainment industry, a stage upon which to play out the story they want to tell. Where actual history interacts poorly with the plot, the history tends to get changed. When what actually happened conflicts with what people believe happened, most filmmakers will default to the misconception, since that is what the audience expects. While it would be nice if films were most historically accurate, that isn't what they're designed to do.