There are a few possible reasons why someone might ask why you unfriended them, and the best way to respond will depend on the context. If the person is a close friend or family member, you can explain that you needed some space on social media and didn't want to see their posts for a while. If the person is a casual acquaintance, you can simply say that you don't really keep in touch and don't have anything in common. In either case, it's best to be polite and avoid getting into a long discussion about the reasons why you unfriended the person.