This is a quote from one of my favorite movies:
"There are nearly thirteen million people in the world. None of those people is an extra. They're all the leads of their own stories." - Synecdoche, New Work (2008)
Why didn't he just write:
"There are nearly thirteen million people in the world. None of them is an extra..."
I have the same problem when I'm writing fiction. When to repeat yourself and when to use a pronoun?