Trivia: At the very end of the film, when the group uses the Improbability Drive to go to the Restaurant at the End of the Universe, there are a lot of images that flash onto the screen when the drive is activated, so in the other parts of the film. In this case, the very last image shown is the face of Douglas Adams, the creator of the Hitchhiker series.
Trivia: In the planet construction facility, one of the planets resembles Douglas Adams's face.
Continuity mistake: In the scene where Arthur is lying in front of a bulldozer, he is so close that his hand is touching it. Two shots later he is a foot away from it, without appearing to have moved at all.
Chosen answer: Because it was a radio show originally, Douglas Adams would write broadcasts from show to show. He did not know where something would lead, which let the plot become random and funny. So ultimately it was originally created to be funny, then he found a way to link it back in later.