Why do people ask a question and then delete it a few minutes later?

In a lot of cases, especially if the person asked a chat question, it was probably reported. Hence the question is no longer there. However, if I have done some research and the question appears to be legitimate and there seems to be no reason for its deletion, I will e-mail my answer to the person if he or she permits e-mails with a little comment that I thought they might want to take a look at my answer. Most often I do not get a response but still I at least get the satisfaction that after the effort put into my answer, the person will get to see it.