James Cameron made "Titanic" because he thought he could convince the studio to let him film the real ship, he confesses in an article he wrote for Wired. "Making the movie itself was actually secondary in my mind," he wrote. He goes on to say, "After the success of the movie, I found myself less interested in Hollywood filmmaking and more interested in the challenges of deep-ocean photography and exploration."
If you ever wondered why he hasn’t made a real movie since "Titanic," there’s your answer. He talks about his love of diving and his need to explore, but mostly, he’s trying to make the case for exploration in general and space exploration more specifically. "Exploration is not a luxury. It defines us as a civilization."