
Visible crew/equipment: At the Quidditch match, after Hermione sets Snape's cloak on fire and someone shouts, "Fire! You're on fire!" there is a close-up of Harry with his hands gripping the Nimbus 2000. In this shot, the wire rods which are attached/taped to the broomstick, near Harry's fingers, that lead under both of his red sleeves, are entirely visible. (01:21:35)
Chosen answer: There are several reasons. First, the position is cursed, so there is little reason to give Snape the job when he will not last any longer than all the previous instructors. If Snape did become the DADA instructor, something could happen to him that could result in his being harmed, having to leave Hogwarts, or be otherwise incapacitated in some way; that would render him useless to Dumbledore as a double agent. Also, Dumbledore trusts Snape, but putting him in an environment where he is teaching about dark magic on a daily basis would be too tempting and emotionally compromising to someone who had been so easily seduced by the dark side. He could possibly relapse. It would be like having a recovering alcoholic work as a bartender. Of course, he does eventually become the DADA instructor, and lasted no longer than his predecessors.
raywest ★
In the movies it is never mentioned that DADA role was cursed by Voldemort.
This is true; though it doesn't say it's not either. With trying to fit 7 long books and years worth of pages of HP information in 2 and a half hours; as long as the movie doesn't say it's not cursed, with our knowledge, there is no problem with reporting that it is. Even directors of non-book movies do this all the time; leave background information out that helps explain things they just didn't have time so they explained it behind the scenes.