Simple - because the government doesn't have the ability to forbid consenting adults from having sex - it's a fundamental human function. Mom might not be allowed to KEEP a child carried to full term, once child protective services was made aware of the existence of a new child, but the state can't stop her from MAKING children as fast as her body can deliver them. The trick is, as you noted above, that since the state doesn't have a monitor on mom's uterus, they generally won't KNOW that mom has had additional children until they are notified of such. In rare cases, like in small towns where the ob/gyn might be aware of mom's history, such a report wouldn't be made automatically at birth, but would depend on either some person knowledgeable of the circumstances to report the new arrival, or, sadly and more commonly, until mom's poor care for her children came to light with some victimization of the new child. Unlike sex offenders who might be subject to chemical castration, neglectful or abusive parents don't face similar sentencing that would prevent them from making a new round of children to neglect or abuse. If only....

