I'm gonna say its that there are more things to consider beyond the plot
Explanation:
when you read a novel, you can imagine what's happening but when you watch a movie you can see it yourself and see the facial expressions of the characters and body movements and can tell their feelings. It could be more than just the story's plot, maybe being able to understand what exactly is happening by being able to see it happening for real and not in your mind where you just make it up.
