Your writtten English is very good, and you seem to have little trouble with television "sit-coms" (Situation Comedies). I think I can suggest another reason you have a problem with some of the movies - because I have the same problem.
Lately I've been having a heck of a time understanding the dialog in a lot of movies. By the way, English is my native language. I was born and raised in Chicago. But now, when I rent DVDs I find that I have to replay many scenes, sometimes several times, to understand what was said. At first I thought that maybe my hearing was going bad - I'm an old guy - LOL. But several of my younger friends claim they have a similar problem. So we watched a couple older movies, then a recent movie and figured it out.
Zooey is on the right track with her explanation (above). It is the way movies are produced. Among other things the volume of the background sound, especially the music, is so loud that it obscures the lines spoken by the actors.
Try this yourself. Watch a movie produced 10 or 15 years ago, then watch a recent one, even something like the last "Pirates of the Carribean" movie and you'll see what I mean. It is as if the producers think they need to amaze us with special effects and sound instead of giving us some dialog to think about.