I'm currently in the middle of a graduate class in the anthropology of religion. We were talking about converts to evangelical religions (my professor works with Maya populations in southern Mexico) and the point about disenfranchised and powerless people (poor families, women) is the generally accepted answer for why people join.
Kudos to ya, asleif!
Yep, their looking to make something out of a life of little or nothing. But there's nothing but hot air to build on.