A person's friends, family, social support... and frankly, modern culture can make moving a sticky problem.
https://www.census.gov/library/visualizations/time-series/de...
The rate of people moving between states has dropped significantly.
https://www2.census.gov/library/visualizations/time-series/d...
The people moving within the same city has stayed rather constant, it is the distance moves that have dropped - https://www.census.gov/content/dam/Census/library/visualizat...
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I believe that if you offered homeless people in Oakland a job and a house in Kentucky that they could pay off in 10 years while working as a dish washer, you would have very few takers.
I would also suggest that the town that has the dishwashing job in Kentucky - that business is likely to close in 5 years and there won't be any more unskilled jobs in the town and they'll be out of a job and unable to pay the mortgage, get foreclosed and be homeless again -- they know that story.
Better the devil you know than the devil you don't - homeless in California is known while a homeless in Kentucky is something else with even fewer opportunities out.