Good explanation of why it's optional in this case, although i'm not convinced that reason is the only reasonable antecedent of why. For example, the explanation why is a common usage,. I have flunked the exam, that is why i am attending coaching classes. I have flunked the exam, which is why i am attending coaching classes. Is there any change in the meaning of sentence.
Why does everybody want to help me whenever i need someone's help? Can you please explain to me. Why is used here as an interjection. According to merriam-webster: —used to express mild surprise, hesitation, approval, disapproval, or impatience I don't think as to why means anything more. It's a rather unusual term except in poetry where you need a bit more emphasis - or a couple of extra words to make the lines line up.