I feel gloomy

Today is little cold, I go to coplay to change the size of my clothes.
After I go out of the subway station, I see two persons, whose clothes are dirty, standing on the street with a cardboard.

At first time, I don't care because I'm hurry to change the clothes. But when I come back, I find they are still there. Then I see what said on the cardboard.
I find some information about them:
They are father and son;
They are homeless now;
They need help.
Those are also my reasons to help them. When I go closely, I find no one pay attention to them, although there are many people around the street. When I see their eyes, I can find sadness. I give the father $20 that I have in my pocket, and I hope that may help them.

On my way home, I'm still think about the "Thank you" he told me. I have a question about "why people don't help them?" Because they may not be the real homeless people? If they are the real ones, what's the future of them and what can we do for the homeless people?
I need an exact answer.