I seriously considered this when I was between jobs about ten years ago. I still wonder if it would have been a good choice.
I'd have to say, anecdotally , that there is a percentage of people on the street that have truly fallen on hard times or mental illness of some sort has put them in that position. The others probably range from lazy to stupid. Most likely both. Then there are the business minded like that young lady. She's putting on a show and people are paying her for it. They are buying their own little piece of 'guilt relief'.