As TomB_2012 said, some people don't want kids. I don't want kids.
I was raised an only child, in a quiet home. I didn't have brothers or sisters so that I could learn how to care for a baby. And I hate noise, which children make a lot of.
And Chadtreme, you obviously have no idea what it's like to care for one child, let alone several. You have to buy baby formula, toys, diapers, doctor visits, baby food, baby clothes, and it doesn't get any cheaper as they get older. You have to continue buying them clothes until they are well into their teens, because they grow and will constantly need new clothes. Not to mention all the gadgets that every child must have (and will periodically need replaced) such as computers, mp3 players, cell phones, and video games. That's just a few of the expenses with raising a child. Just imagine doing that with ten to twelve children!
And then you have the messes they make, and the money replacing stuff they damage. You have accidents, such as maybe breaking a bone or getting stung by a bee. And then there's the crying when they're young. I can't stand to hear a child cry.
And all these things together, makes me not want kids. And if I had a child, I'd probably put it up for adoption. I may have a hard time finding a man who doesn't want kids, and unfortunately, I'll have to turn down any nice men who want children, because that is one thing a couple must agree on.