I have three stories in the movie section. Two based on Star Wars, and one with Predator as a central theme, as well as some other characters that have appeared in movies, but also none movie characters.
I suppose a difference between movies and TV is that you often only get to see characters for 1-2 hours in a movie, where as on TV you have 12 or 13 hours a season, and sometimes more.
Given the amazing business Titanic did, I am surprised that there are not more fanfics for it. I believe it is still one of the highest grossing movies of all time, if not the highest.