Why are women not treated like men?

Answer: Because women are not men. Nor can they be like men. They can try but then they become transgender and may therefore be treated like women trying to become men.

Answer: While it's true women aren't men and that's part of the reason women aren't treated like men, it's also due in part to women being seen as the weaker of the two sexes. So, sometimes people, including other women, feel they shouldn't always treat them equally but treat them in manner for lacking whatever they believe a man has.