JWs are instructed in recruitment methods that specifically target vulnerable populations, such as adolescents learning to be independent, college and university students who may be away from home for the first time, people in troubled relationships, separated, divorced, the impoverished, serious health problems, people who have just had a major move and have no local support system, families with new babies.
It's no surprise that the majority of recruits come from these types of backgrounds, because those are the ones being targeted.