in one word: its just *culture* sister
in Islam, men and women are equal when it comes to rewards and sins. eg. salah, fasting, equal punishment for stealing or sexual relations before/outside marriage.
its just the soceity which have created the mindset that if men sins, its okay but if women do the same she is immoral,etc. if a man drinks or smoke or have opposite gender frnds...he is not looked down upon as much as if a woman do this.
these things have no place in Islam.