The answer is absolutely "why," and really can't be "when." "Why is it that no one listens to me anymore?" is a completely natural English sentence. As Lackadai says, it would be /possible/ to imagine someone asking about the specific times when no one listens to them, but a) this would be a very strange thing to ask, b) this would be a very awkward way to ask that question, and c) even if you did ask the question "when," you would have to remove the word "anymore" in order for the question to be grammatically correct.
I agree with Bramwell -- the book you're using seems to have some serious mistakes. It would be better to find a different book to learn from, if possible.