Well, there isn't really an easy answer for HOW things got that way, if that is what you are wondering. Patriarchal societies pop up all around the world, so figuring out how they got that way isn't easy (not something I have an answer for).

If you are looking for a LEGAL reason, then you might want to look at the concept of pater familias. This is basically the male head of household that has nearly unlimited legal power over other people in the household. This would generally be the oldest living male in the family, so if a father died it would go to the oldest son, who would have legal authority over his mother, then. Again, why this was male dominated isn't something I think anyone has an answer for, as male dominated societies tend to have their roots in pre-history.