Here I explain the inexplicable. The age old question of why parents pressure their adult children to have children of their own. In short--The Grandchild question.
It's simple. You, the adult child, will one day be old and decrepit. When that day arrives you'll need someone to look after you. If you've made millions upon millions you can be as baron as the moon. But most people are poorish. And so they need adult children to lean on. Of course the bringing a child into the world does create some emotional attachment. The elderly though, not yet decrepit feel a little guilty about what they are about to put you through in a few years and think you, too should have that safety blanket. A person can't come out and say that. That sounds awful, so, instead, they just say, "Have kids. I want grandkids." Without any real reason to do so. Usually, given as a reason when pressed is, "Children are a joy." We all know that's not true. They're needy and time consuming and make you put your dreams and life on hold. But all that work and sacrifice is in an investment in your future. You're future of not being able to walk or see, or maybe even remember anything.
People may criticize this theory in the fact that the grandchild was something people were pressured to give to the older generation prior to us living until we fell apart. Yes, but back then children were needed for farm labor. Again you can't just come out and say, "You need to birth your own slaves."
In conclusion I leave you with this question that I'll answer. Why do you think gay people are pushing so hard for the legalization of gay marriage? Married people have a better shot at adopting a child. And don't gay people need someone to take care of their decrepit asses too?