Famed screenwriter, William Goldman has said, and as seen in this clip, the following:
There is undeniably an adversarial relationship between writers and directors. in movies. Nobody messes with the composer because not everybody can write songs. Nobody messes with the cinematographer because nobody knows how to light things. [But] even producers know letters and alphabets and directors and everybody like to fiddle [with the screenplay]. [It] makes them feel creative.
One of the reasons there are no happy screenwriters is because you have all those people who think they can write better than you can and many of them can and many of them cannot and things [screenplays] get altered. There is this lunatic myth... that the movie is the director's, and that is about as much sense as the flat earth society, and everybody in the business knows it. I'm not saying it's [all] the writer's God knows it. I'm saying that movies are a group endeavor.
Oh I get it. If you can pass 2nd grade writing class, you're a writer. I guess it's ok to pay these people in lollipops.