What do you make of the birth rates being much higher and stable among married couples, and of the birth rates among women in their 30s increasing? These don't really correspond to your take.
People in their 30s, married, tend to have more stable lives. They are in a position where they feel they are able to give that child a good life.
This is the number one reason for the decrease in fertility. Unplanned pregnancies are becoming a thing of the past.