Why are women not allowed to go out alone even in today's society?

Men are allowed to go out to anywhere they like and at anytime they wish. Women on the other hand are restricted and can only go out with a mahram by their side. I understand that this is because men are obliged to protect women. However in today's society women can go out without needing protection, especially at times of day light. Also what if the men are at work and the female needs to go out for something?