Back in ye olden times, you would pay a bride price to the parents of the bride, both symbolizing the eternal debt you owed to your wife and as a way to show you had plenty of money to spare to take care of your wife. You would then give your wife a dower, sonething they could hold onto in case you lost all your money or she became suddenly widowed. This historically was property but became rings or jewelry with expensive stones. The wife would take the dower as a sign she would no longer need to worry, and in exchange be a maiden on her wedding night. These practices were only for the wealthy, until indistrialization brought the practice to a growing middle class. Then, in the early to mid 1900s, marketing campaigns began associating the price of a ring to the love you felt for your wife, leading us to today.

Doesn’t prevent it, but gives the girl collateral if the guy breaks off the engagement afterwards.