Fear of death and non-existence. Spread memes not genes. Socrates' heirs are not apparent, but his ideas linger strong. Although most conceptions are unintended, a desire to conform to what society considers normal is probably the number one cause of wanted pregnancies. Many who continue to breed have never considered doing otherwise.
Natalist propaganda remains rampant and insidious.
Q. I've always wanted to have a baby of my own. Most people who aren't already parents need alternatives to fill the needs which procreation seems to fill. For those who prefer not to substitute Nature for humans, there are plenty of children in need of parenting. Also, occupations in child care and education can provide ample opportunity for sharing and caring. Young people aren't the only ones in need of care.