In many cases people on the streets had strongly family ties, up until their mental illness began to manifest and their family was no longer able or willing to continue supporting them. People get kicked out of their houses because of violence, financial hardship, or any of many other difficult reasons. It's not simply a matter of people lacking compassion.

Take the case of the late Terry Davis for instance. He was living with his parents for years, but their relationship deteriorated as his illness progressed and in the end he died homeless. I don't think you can rightly blame his parents for that.