Trivia: Originally Obi-Wan Kenobi survived the duel with Darth Vader and fled aboard the Millennium Falcon. But the character had very little to do with the rest of the film, and George Lucas decided that he should be killed off. Alec Guinness threatened to quit the production over the change, but Lucas convinced him that the change was better for the overall story.
Trivia: Sir Alec Guinness was apparently not a fan of the Star Wars dialogue. A letter was found in 2016 that he wrote to his friend saying "New rubbish dialogue reaches me every other day on wadges of pink paper, and none of it makes my character clear or even bearable."
Trivia: Princess Leia and Obi-Wan Kenobi never meet once in the entire film.
Trivia: When Luke is the climbing the ladder to his X-Wing fighter before the Battle of Yavin, an InCom Engineer asks him if he needs another Artoo unit. This engineer is Shane Rimmer, best known for the voice of Scott Tracy in the Gerry Anderson series "Thunderbirds".
Trivia: Scenes with the Jawa sandcrawler were shot near the border of Tunisia and Libya. Worried Libyan officials looked over the vehicle to make sure it was not part of a Tunisian military operation.
Trivia: Although Peter Cushing is listed as Grand Moff Tarkin in the end credits, he is never referred to as either Moff or Grand Moff. Throughout the film, he is simply called Governor Tarkin or Tarkin.
Trivia: Before being cast as Darth Vader, David Prowse was offered the role of Chewbacca. Prowse turned down Chewbacca, as he did not like the idea of having to wear a furry monkey costume for his part, so he chose Darth Vader, as he believed that everyone remembers the villain.
Answer: Presumably because the monster has pulled him through the lair of whatever they are standing on into whatever space the rest of the body of the monster lives in. Obviously, the monster doesn't live in the part of the part of the compactor that does the compacting or it would be already compacted.
Myridon