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.