Upon moving to a new city, for whatever reason, be it a job transfer, life change, or just wanting to get away, many people don't know others in their area and may have a hard time assimilating to the new environment. They may have trouble connecting with their associates, coworkers, or other people around them, which is why the idea of a cult is so appealing to them. The offer of a group of people who are willing to accept and befriend is quite appealing to those in a confused, fragile state of mind. Though nowadays they're not called cults, since that has a negative connotation, but other names, like self-help groups or clubs.
A less drastic example would be high school or college freshmen. They're thrown into a strange situation and will most likely seek a group of individuals like themself to associate with.
The psychology here is not difficult to understand: a person in a new situation seeks comfort from like-minded individuals. Once in a group or "cult," they are further indoctrinated and solidify their membership. Groups like these know that people are vulnerable in a new situation and use that to their advantage in recruiting new members.
Cults seem to take advantage of those that are vulnerable. They seem to identify their weaknesses and create an environment to nurture the person . Once the person feels comfortable it may make it really hard for them to recognize the situation for what it is.