That movie was so bad - it seemed to me like most of the actors were just reading their lines for the first time, and then George Lucas goes "CUT! OK that's good, let's go make more dresses for Amidala".
It's like someone doing a presentation for the first time and reading what's written on it line by line vs someone doing it for the 100th time and going "fuck the slide, now let me tell you a story". It takes a while for actors to figure out who their character should be and how the character would and should act.
And that sort of thing results in Han Solo's famous in-character "I know" to Leia's "I love you" instead of the boring forgettable "I love you, too" that was apparently in the script.
That's why you hire actors - for their input - they'll tell you that their character shouldn't do X and should and would do Y instead. They might not always be right, but the good ones often are since they're focusing on that one character whereas you as the director are doing a lot of other things. The original writer might write a lot of stuff that works in a book, but doesn't work in a movie.
Someone earlier said acting was lying. But it's a higher form of lying where you are true to the character. Just like the Joker hospital explosion scene when not all the explosions went off as planned, and Heath Ledger improvised and turned the fault into a cool feature.
A nonactor like me could "tell the same lies" but not be believable as that character at all.