I can understand why some would... I don't, but I might consider it. I can't count the number of times that I've answered a silly question and gotten positive feedback galore... and then spent half an hour researching a question for someone and not gotten so much as a "kiss my foot" for my troubles.
Because people..... Get this... Don't know the answers to the questions they ask. There are people who ask hard questions and also answer hard questions. Easy questions get easy answers. Not everyone is going to answer your question on your physics or chemistry homework for you. I apologize buddy, but I'm no tutor.