Because these books are riddled with it.
Now, don't get me wrong, I've read books with plot before :-) But these books have a PLOT. Sure, they've got story. Sure they've got themes. And they've got characters. Most books do...imagine that. But when I say that there's a plot...well...there's a PLOT. Practically every other sentence there is actually something happening. It's happening fast. It's happening furious. It's happening.
Coming from a writer who could have a character stare out the window for five pages, this absolutely amazes me. If we look at plot as a way of getting a character from A to Z, well I'm not sure there are enough letters in the alphabet for this series. It's an impressive feat.
For me, I divide novels into two categories, plot driven or character driven. Of course, these lines are quite often blurred. In The Hunger Games and Catching Fire, for example, both things are driving the reader forward, but plot is clearly the stronger engine.
So how do you find a delicate balance? If you're the type of writer who would rather have your main character sip a cup of coffee for years on end reflecting on the state of the universe, how do you cut it down and still accomplish your goal in the scene? My philosophy these days is get in and get out as efficiently as possible. Get to the next place. Get to the next person. Move your character as quickly as possible through their story, sitting in the scenes that matter and getting out of scenes that don't. But the question is...what matters? What doesn't?
While I figure that out, I'm happy to have read Catching Fire this week. If there's ever an example of getting in and getting out of a scene like rapid fire, Suzanne Collins is the big winner. Not Mikey. Suzanne.