There are lots of reasons. A culture, a family, even a churches future depends on the next generation. More people means more power, more resources, more clout. A culture, any culture, must be concerned with how many children are born and the stability of the homes these children are born into, because this defines the culture in many ways. For me, looking at gender rules in the context of this reproduction and rearing of children seems to make sense.
Girls are sexually desirable, mothers are stable, and so on.
There is of course overlap in these roles, but they show the woman going though the process of being a responsible and valuable person who reproduces in culture. The Roman Catholic church holds Mary up as the ideal woman, a mother who played her role in bringing new life into the world. Men in the church were required to stay married, not because of desire, but because they had an obligation to their family, a role to play in the child rearing function. Women got home and children, men got money and property, and together they made a big family that honored God and expanded the power of the church. Even today, the agrument made against homosexuality is that it is inherently non- reproductive, therefore it is wrong.