Why do some Muslim women not wear scarf?

Men and Women are different, therefore rules must be different in order to suit each of them. Where men and women are the same they need to do the same things, for example; praying will not cause either any problems so both are obliged to do it. However, for example; women generally need to look after children, therefore do not have to go to Jumu'a (Friday prayer), whereas men do. Men's desires have scientifically been proven to be much stronger than women's, therefore to keep temptations as far away as possible for them, women are required to dress modestly. Men must also dress modestly in covering themselves from the knee up to the belly. So, where men and women are the same they must give the same, where they are different, different rules apply for each.