Up until the mid-20th century, it was basically required literally everywhere to cover your hair and dress modestly as a woman in every middle eastern and central asian country. It's the traditional style of dress. While I doubt that it was written into legal code, it was just the way that women dressed every day. Pictures from Egypt and Iran in the mid-1900s feature women in western dress because it was coming into fashion, but these were almost always rich, cosmopolitan women. The vast majority of peasant women and women in villages still covered their hair. Eventually, a good amount of urban women started wearing Western dress, but there was never some type of free liberal society going on. And a few years after not covering hair became 'in', there was a resurgence of headscarves and political Islamism. The point is that the headscarf and religiousity of the population never went away, it just became slightly more acceptable to not cover yourself in certain cosmopolitan areas.