In my opinion urban legends gain wide circulation when they meet emotional needs. But what needs do these meet? I think there are three, and I must add that I am not making a point here about American people, but about people.
- simple racism
- simple selfishness: finding a rationale for not helping without pesky twinges of conscience
- a wish to see the world as reflecting rational and moral order
That third one is the most interesting to me. I've hung out with New Age types, and they have something in common with Calvinist protestants. They think that your destiny reflects your worth. Life as a system of rewards and punishments for choices. Lots of films and books express this idea, and it certainly satisfies me to see the baddy get his comeuppance.
The notion does have a true side of course - a clever or determined person can gain advantages over the simpler and more relaxed. This isn't a moral consideration though.
'Moral order' is a popular idea with groups of people who are in the ascendance. During the British Empire some Victorians thought the English were morally and intellectually superior to other countries. I think, probably for similar reasons, it has more credibility in the US at the moment than in any other society. It is surprising to see it expressed so widely and unselfconsciously.