I know you're not supposed to judge a book by its cover, but on a limited budget one has to make choices. This bias could hold true for many of Avalanche's products, and is not simply based on sexism of the cover image as I've shown.
On the sexism note, I should make a few brief points. First of all, someone indicated that there were no scantily clad women in history. That's simply wrong, for many eras. The book Nile: War in Heliopolis is inaccurate historically because the woman is wearing too much clothing (though, ostensibly, she could be wearing an Egyptian (Kemetic) robe, many women went topless in ancient Egypt). One might also note that some recent releases by Avalanche don't have such risqué covers (I, Mordred, All for One and One for All, and Vlad the Impaler Blood Prince of Wallachia).