Of course, even when the selling point for a given film is something other than the director or creative team behind the movie, we still show an interest in learning more about the process of making the movie. This is enjoyable for, and now expected by, consumers, but it also makes sense to the studios, who like to give us as much incentive as possible to buy the DVD by loading it with things you can't find anywhere else.
For example, commentary tracks give us an inkling of what the real actors who made the film are like, rather than just the characters they play. Tracks also give the director and producers a forum to share their own thoughts. This can add greatly to our understanding of the film, as well as our understanding of the art of filmmaking itself, and these types of features are often the main attraction when we consider buying a DVD version of a film we've already seen.
It's also common to include a documentary feature detailing the process of making the movie, whether broken down by category (special effects, makeup effects, wardrobe, etc.) or, sometimes, in longer featurettes with their own impressive budgets, directors and talent. Many films now come with a separate disc -- another 5 gigabytes! -- to contain all the special features that were created alongside the finished film itself.