The "problem" here is people here are profiling without being so aware of it.
When someone who looks homeless hits the ground looking for help, there's still a chance they're trying to get something out of the situation. I've seen homeless people feign injury many times to scrape up cash from sympathetic bystanders, or to try securing a bed in a hospital for a night. That kind of thing makes people numb in their reactions.
There's also a potential for harm. Many of the homeless are mentally ill and I'd be slow to offer a hand for fear of my own safety. Seriously - I've seen them physically attack people for no apparent reason. That said, if I got the feeling something was truly wrong, I would certainly call the police and send for help.
When someone is clean and dressed in a nice suit, and they hit the ground calling for help, they're much less likely to be doing it for the purpose of simply getting attention or some extra cash.