It could be because authors imagine highly developed world building isn't something of great interest to your average teenager, whose understanding of the world is based largely around their experiences with school, friends and family. The target audience for the Hunger Games- some 12-16 year old female American, isn't going to be terribly interested in the political and economic aspects of the fictional world that don't immediately concern the characters, let alone what happens in other places like Europe and Asia.
That said, I can think of some good examples of highly developed worlds (I.e- Star Wars universe) that certainly capture the interest of young people, so I wouldn't really agree that teenager's aren't interested in fictional worlds outside of their real life experiences.
I think though that highly developed world building for dystopian teenage fiction isn't something high up the priority list for the authors- far behind things like plot and character building and the general concept behind the novel.
That said, I can think of some good examples of highly developed worlds (I.e- Star Wars universe) that certainly capture the interest of young people, so I wouldn't really agree that teenager's aren't interested in fictional worlds outside of their real life experiences.
I think though that highly developed world building for dystopian teenage fiction isn't something high up the priority list for the authors- far behind things like plot and character building and the general concept behind the novel.