"Which of us has not wondered, on exiting a movie theater on a summer evening after viewing a real stinker: "How on earth did that ever get made?"
I have been involved in the movie business now, at least peripherally, for more than 20 years, and while I still can't claim to fully understand it, I think I am now in a better position than most to answer that question.
Fear is the first and biggest answer. It costs millions to make even a small film, and most ultimately lose money. So producers and studio executives begin hedging their bets artistically the moment an idea for a film is conceived.
In fact, with many movies, the hedging begins before the idea, in the case of "vehicles," films conceived for the sole purpose of putting a momentarily hot box-office star on screen. Miley Cyrus comes to mind, or Seth Rogen or Lindsay Lohan. Needless to say, the more expensive the movie, the more hedging.
One of the first big ways of hedging your bet is to never do anything original. Original means risky. This is why sequels are so popular. If they could get away with it, studios would release the same film each year with a different marketing campaign. This pretty much explains the Rambo series and Pirates of the Caribbean."