[NTDF9]

A few reasons:

1. Weather in most northern states will cause death

2. Transportation for poor doesn't exist in the US

3. If one can't find jobs in SF, forget about being able to find them in Tulsa. Reasons vary from number of employers, lack of transportation, lack of education, felony record, divorces/child support.

I think the easiest way for someone to imagine this would be to think os the US as a dense jungle. The bounty is plentiful but there are death traps everywhere. Only the death traps are man made.

You need to find the patch of this jungle where you are likely to survive. Which means living under a rock in region A is better than dying in a barren desert in region B.