I think because the contributions of women haven't been as "glamorous" as men, they've largely been forgotten. It's often forgotten or ignored that women were the head of the household and on a day to day basis were vital to the functioning of society. They were the ones that would dictate what happened to the family's resources. They were the social hubs of each household. They had direct influence over the most powerful people, they were the mothers and sisters and wives of every powerful male. They were totally in control of how children were raised (think about that, the entire next generation was raised almost totally by women)
So yes while they may not have contributed as much to specific fields such as science or arts ect, they have always been absolutely vital to society (beyond the obvious child bearing roles). You have to remember that most people throughout history and weren't powerful or "gifted" and it's the day to day plight that's shaped society more then anything else. So I do disagree that women have contributed less then men, in the past anyway. I don't like modern gender politics and would rather not comment on the current dynamic.