Harry canonically disdains "people stuff", and while some of that may be an act for Draco, it does seem in character for him to be more interested in the sciences than the humanities, more interested in learning the rules by which magic operates than facts about the past actions of people who have operated it. As I recall, the only reason he knows so much about the historical decline of Slytherin House is that it came up in the course of his research into the Patronus Charm.