Also, according to other comments here, many shelters either require houseless people to turn over their belongings (cell phones, medication, paperwork, etc.) to the shelter for "safe-keeping". These belongings can then frequently "go missing", forcing the person to start over from scratch. Alternately, shelters without this policy in place expose the person to the risk of theft from their bunkmates.

The combination of these two factors leads some to self-assess that they're better off on the street.