I believe there are researches being conducted to understand this behavior but to me, I don’t understand why people would want to behave or act in a manner where they have absolutely no control of what they do or think. According to the standard understanding or definition, a zombie has no sense of feeling or experience. It is this sense of feeling and experience that actually defines humans. It is the core to who we are and I don’t see any reason why people would want to give it up or pretend to do that. A vampire sub-culture is something that makes more sense and is close to human nature than a zombie sub-culture.
Even though it is up to the individual to decide if they want to be part of a zombie sub-culture, but I strongly feel such sub-cultures explore the dark and negative side of humans and must be not be encouraged. It can have negative effects on society as a whole.