My guess is it comes from drug related policies, education, culture and enforcement. The USA is the developed country with the highest per-capita rates of alcoh

My guess is it comes from drug related policies, education, culture and enforcement. The USA is the developed country with the highest per-capita rates of alcohol & drug use disorders and drug related deaths. I believe this is due to the geography and high purchasing power of americans, not due to any flaws in character. You're in a place it's easy to get drugs into, and people earn enough to buy them. This then creates a mental health and drug epidemic which are the true cause of most homelessness in the cities you reference, as opposed to purely being lack of money, job or housing, though these problems are obviously not mutually exclusive.