In the past, unmarried girls who got pregnant had to be supported by their families and relatives. It gave the whole extended family an incentive to ensure it didn’t happen, and to tell young girls the bad fate that would await them if it did happen.
Civilization is all about parents instructing kids about consequences. Remove the consequences, and the kids stop listening.
If girls knew they would have to support the baby by going out and getting a job (or starve), they would stop having babies outside marriage to a steadily employed man.
There are plenty of cultures and times where reproduction bore no relationship to the ability to provide.
Given over to their nature.