If the argument is how people become homeless, rather than why they stay homeless, we need to be a little bit careful with causal direction. Some people become

If the argument is how people become homeless, rather than why they stay homeless, we need to be a little bit careful with causal direction. Some people become homeless because they are mentally ill and can't maintain a tenancy. Some people develop a mental illness after becoming homeless because it's living on the street is pretty stressful.