Poetry

Why not?

A screenwriter must derive the most impact from every word in a script. That makes screenwriting like poetry.

If you're lucky, so inclined or talented, even action lines have rhythm.

A script page looks like a page of poetry and not like a block of prose.

Because the purpose of a script is not to make a movie.

The purpose of a script is to get readers, one after another, to fall in love with the characters, to see the pictures, to feel the story.

If you can do that, the movie's gravy.