"why should we expect a guy to work late in the night, come on weekends, push hard deadlines and a girl is given all options to leave early?"

Well, to put it drastically: biologically men are almost worthless. They can not produce babies. Hence women can make higher demands. Men have to bid for women (to carry their children) offering as much "worth" as they can. Nobody has to bid for men, because men are easily replaceable. Especially now that physical strength is not so important for survival anymore (we have guns).

In many species the female actually eats the male after sex for a nice protein boost. That is how useful men are.