said by RockCake:Sometimes the studio's only want one vendor showing a movie at a time so they might remove it from Netflix to show it on Amazon Prime or Hulu for example. Netflix isn't the only company with agreements to studio's after all.
What bugs me about Netflix's movies is the seemingly haphazard way of distributing series. Right now, they have Mission Impossible 1, 3, and 4, but not 2. Starship Troopers 3 (Marauder) but not 1 or 2. I can watch Paranormal Activity 2 and 3, but not the original. Transformers 3 is available, but not the first two. It makes no sense.