The common explanation I've heard is sperm is cheap, eggs are expensive. This leads to the ramifications of men being considered disposable compared to the lives of women where hard labor isn't needed as much.

Men get drafted and get their arms and legs blown off, women can stay home. Spare the women and children in war.

I don't think it's cultural. Most men have an innate desire to protect women, and treat them with special favor. This was the historical way women were protected before they had voting rights. Now, they have both political power, and men still tend to give them the special favor they had before. So it leads to an imbalance in society

There is a cultural side to it like "Women and children first" in emergency situations. I wonder if that is still expected or considered part of the "not correct" behavior? After all, it goes absolutely contrary to the whole "equality" idea.