Why do Muslim women think they only way to dress "modestly" is by covering their entire body with fabric?

It is because their Quran tells them to. They consider even showing their face and other parts of their body as a form of prostitution. It is said that they feel that the face is the most tempting part of the body and by revealing their body, they anger their god. Even if a girl doesn't believe in this, she will have to wear otherwise she will be fined, beatened and even killed...