Earlier quoted context omitted.
Quite a few are homeless by choice. There are shelters available but they choose not to go because the shelters ban drugs. So they choose drugs over shelter.
Shelters also ban lots of normal things that make them harder to use, or have onerous rules around your schedule that make working impossible. There are a lot more reasons people don’t use shelters
When I was there, I counted about 2 drug users out of 100 people in a shelter in Spokane, Washington. The rest were either ex convicts, disabled/mental issues, or just simply lost their home.