The Human Need to Parent
There is a natural parenting or child rearing instinct to one degree or another in all of us.
If we mistakenly assume there is an urge to have sex only, and that having children is merely the inevitable outcome that we must deal with when it happens, then we are neglecting an important factor in human motivation. With the availability of effective contraception, we could satisfy sexual urges while avoiding the consequences if becoming a parent were not a motivating factor on its own.
When we have poor urban teenagers having children, it is not that contraceptives are not available or knowledge of their use lacking, it's that becoming a mother is desirable on its own despite their disadvantaged situation.
Women who have focused on a career who find that even the marginally acceptable men have already been taken, none-the-less find a way to have children, on their own, if necessary, when they are ready.
People who are asexual may marry due to their desire to have children in the socially prescribed manner. Some asexual women may not be aware of the sexual attraction that other women have for men. They may accept having sex as a duty rather than a pleasure and would rather avoid sex with their spouse if they could. This displeasure may reach the point where they refuse to have sex any longer. Their partner will either have to live with that fact or find someone new.
More in the past than today, gays have married someone of the opposite sex to fit in by having a spouse and as a means of having children. Sex with their spouse is no more a pleasure to them than it is to an asexual person.
Neither a fatherless home nor a loveless marriage can prevent some from being a parent. Now that gays have more choices, it's not surprising that they would want have children as before, but to love the person they marry as well.