Also, movies are released at different times to different parts of the world. The studios want to get all the money from every theater they can first, anywhere, before they put something out on DVD. Plus, the film needs to be remastered for DVD, audio commentaries and extras have to be added, art direction done, etc. It’s a lot of work and bureaucracy, as well, because departments have to sign off on things, the lawyers are involved, etc., etc. These activities all take time.