Because some people feel that they have emptiness in themselves that they feel will only be filled by doing something worthy of credit to themselves. Others do it out of pure good will. Everyone needs something to complete themselves...
Because not all poor people choose that route. My family is bordering on poor. No one has any right to say my parents do not work hard. We needed government help at once point. Do you think that, just because we are poor, we do not deserve help?