Turkish here! The reasons are the fact that we are poor as fuck to finace a newborn baby and the financial incentives of marrying. When you marry usually the tradition is like the bride side funds the ceremony and groom's side funds the house goods like dish washer, bed etc. You also get lotsa assets from your other relatives, colleagues, and friends. Moreover, both grandparents, being rich boomers, subsidise the cost of grandchild and take care of them. They wouldn't do so if it was outside marriage because of old school mindset (herritage laws play a big role here too).