Could it be the "Blue" states offer more services to the homeless and people emigrate to these states because their state doesn't offer any services or "Blue" states have a bigger population? Maybe people are homeless because the US government decided to stop investing in affordable housing in the 60s and we're pretty screwed now. Hm or there are not enough jobs and no income means no basic rights and kinships broke down because everyone is just scraping by.

Native Americans might be homeless because white settlers pushed them off their land and murdered them.