Families are great, aren’t they? Families come in all forms and fashions. As far as the nuclear family, the father, mother and 2 children, that works well for some cultures but not for all of them. Some families have the necessity of being larger, say the parents are farmers or business owners and want to be certain that the farm has enough people to work it, or that the business stays in the family. Some just want big families, and others are dictated by their religious affiliation.
Families were large out of necessity. The mortality rate of babies was pretty high before modern medicine and if a man or woman wanted their bloodline to continue they should have many children so that some would survive. Other necessities include parents ensuring that their own mortality will not take them too soon. Parents with many children are likely to have one or more that will care for them in their aging years.
There are religious organizations that prohibit birth control, like the Catholic faith. These individuals are likely to have many children because they wish to continue intimate relations with each other and their devout following of their faith will not allow them to keep babies from being made and ultimately born.
Some people just have babies. They may try birth control, they may try alternative methods of having sexual relations but they are going to give birth to a baby no matter what the precautions are. Abortion is not always an option; some don’t believe in it, some believe it is murdering a baby, so the baby is then born. Birth control pills are only about 98% efficient in keeping a woman from getting pregnant; other methods are even less reliable. Clearly the only way to guarantee that a woman does not get pregnant is to not have sex at all. Multiple births, like twins or triplets, can give a mother a great deal more than they bargained for, too! Sometimes fertility medications will create multiple births to occur.
Some women feel the need to be mothers their whole life. If they continue to have babies, they will always have someone to nurture. Mothers who have babies later in life after they’ve already raised their first children sometimes do it to keep from suffering “empty nest syndrome” where they begin to question their own worth now that their children are grown and gone. Then there are those women who just want babies so they just keep having them. It may be a pathological response to a childhood that was lacking in nurturing, or in a childhood that was over-nurtured.
In all cases, necessity, religion, biology, or desire, the woman makes the final choice whether to have the baby or not.