Because they are physically weaker, but the deal is, you don't segregate. You have to be a man with issues to even talk about women being somehow worse than men, or unequal. They are not the same as men, in general smaller and weaker, but that's how it is. Most men don't feel attracted to women who are taller and heavier than them.
It's important to state that women are in general smaller and weaker, but it does not make them worse. A man cannot give birth, right? Does that make them inferior to women? We could say that, but we don't.
There are many things women do that men cannot, which is why we need each other and there's no need for rivalry between genders.
The only thing I will say women and men are not the same is in the family which the wife is supposed to give the man some level of respect as the head of the family. But as for society I don't think women should be segregated or look less, they have so much role to play which even the men can't even do alone. As the society is concerned I believe in gender equality nobody has it all, what a man has you may not found in a woman and what a woman have you may not also found in a man, that's to tell you we need one another to keep the world moving.