Oh? You say. Yes. Let's take the Hunger Games, since it was widely popular and honestly, really, really good. So much better than the movie. For the purposes of this entry, I'm only going to touch on the first book.
I found a discussion topic entitled "How do you think Panem came into existence? What events occured that made the nation" and thought "okay then, this will be an interesting conversation to have! Now, some people hypothesized, but most people just sounded stupid. "She should have just said!" "Prequel!" "I'm retarded GO TEAM GALE!!!!!1111!!" Notice how my response is the highest-voted one in that thread? People, Collins doesn't have to give us that much back story. It's not necessary. Bad shit happened, we fucked up big time, that's it. You don't deserve more. Let that little bit of unexplained horror add to the overall desperation, horror, and fear throughout the book. Frankly, a prequel would cheapen Collins' entire trilogy unless she could make it stand alone so far by itself that it could be seen not as a prequel but it's own entity.
I used to want to write fiction. Huge, sprawling fantasy series. I used to write a lot in my teens. It's a lot of work and when I started getting really in-depth, I had a hard time keeping track of my characters, their back stories, even geography. Authors simply can not spoon-feed every little thing to their audience, and shouldn't. Another example: Orlando by Virginia Woolf.
Arguably one of my Favorite Books of All Time, it was then made into my Favorite Movie of All Time and arguably one of Tilda Swinton's best roles, ever. Also one of the best book-to-film adaptations I've ever seen.
I was about to wrap this up when I thought about another one that I've heard readers whining about! Curley's wife in Of Mice and Men.
Okay, so I hated this book and I don't like Steinbeck at all, but this one character generates a lot of conversation. Most of it intelligent discussion about alienation, desire for human contact, destruction of the human psyche, unhappy marriages, abuse, etc.. Then some think that Steinbeck was the most sexist thing ever and that she deserved a name. Sigh. People. A name? You're missing the goddamned point. Here's a really good discussion thread that starts out horribly but then smarter people take it over.
So yes, let's put our critical thinking caps on and learn to interpret what we read and realize we don't need literary hand-holding, mmkay?