It was an artistic choice: Cameron on Jack's death in Titanic

It has been 20 years but "Titanic" fans are still angry with Rose DeWitt-Bukater for not making room for Jack Dawson on that door but director James Cameron says the character was always meant to die.
"...the answer is very simple because it says on page 147 (of the script) that Jack dies. Very simple. . . . Obviously it was an artistic choice, the thing was just big enough to hold her, and not big enough to hold him...," Cameron said in an interview with the Vanity Fair.
The director said it is "kind of silly" to still have this discussion but it also shows that Jack (Leonardo DiCaprio) became so endearing to the audience that "it hurts them to see him die".

"Had he lived, the ending of the film would have been meaningless... The film is about death and separation; he had to die. So whether it was that, or whether a smoke stack fell on him, he was going down. It's called art, things happen for artistic reasons, not for physics reasons," he said.
Fans have come up with their own theories to counter's the director's theory that the door could not have supported two people but Cameron disagrees.
"I was in the water with the piece of wood putting people on it for about two days getting it exactly buoyant enough so that it would support one person with full free-board, meaning that she wasn't immersed at all in the 28 degree water so that she could survive the three hours it took until the rescue ship got there.

"(Jack) didn't know that she (Rose, played by Kate Winslet) was gonna get picked up by a lifeboat an hour later; he was dead anyway. And we very, very finely tuned it to be exactly what you see in the movie because I believed at the time, and still do, that that's what it would have taken for one person to survive," he said.