Because a still developing pre-frontal cortex means young people (under 25) fucking suck at making decisions.
You can divorce, sell your house, file for bankruptcy, or move back to your parents' basement, but you can't unhave children after having them. You can't go on a break from your children, even to take care of your own physical, mental, or economic health.
Most people at 25 don't have any of that shit figured out yet, and in the modern day and age, they don't have the support network of grandparents, that prior generations had.
You're acting like any of these are inherently good decisions. They're not good or bad. They're just big and potentially very regrettable.