Why do employment agencies see long term unemployed applicant a liability, and therefore not answer the person's inquiry?

I am a long term unemployed and I am a little bit furstrated about the situation. People have the tendency to believe the worst scenario, so they always think that a long-term unemployed person must be picky or lazy. So they aren't bothered to help you and they don't ask the reasons or if they ask they simply don't believe you. Moreover, I think that the agencies don't except such cases because it isn't an easy task to find work for a long-term unemployed person than to a fresh, up-to-date candidate. So more of the newcomers means more profits.