This is my view on the book/movie.
A LOT of the entire 3 books is Katniss' own thoughts. It's all one long exposition, and memory, of her experience in the world she lives in. Fictional, of course, but it's all told through her thought process and mind.
Sidenote: Do you girls really think THIS much about things?
Anyway, the thoughts of any character must be SHOWN on film. We can't see what they're thinking.
The movie gave some hints to Katniss playing the "games" of the romance. Haymitch talks to Seneca about it, there's the note, and Peeta's final comment. It's all there, but subtle.
Films must SHOW. Books are free to let you see what characters THINK.
Let it go or figure out the difference between books and movies