It isn't illegal to be naked as everybody constantly is but we have different cultures of cover up. On top of that society demands decent behaviour which often borders on total censoring of any skin. All that is totally different from the legality of being nude. And that is totally different from the actual wish of people to be nude in public. Being nude in public or in privacy is often impractical and unpleasant and too cold. When it is actually something desirable and practical we often do not want to get on other peoples nerves who could object to nudity. So in reality it is not a question of the laws.