In your example (and many others, no offense) it’s a female victory celebration.
It serves as a victory party for the females, no doubt.
It SHOULD mark their entry into married life and all the appropriate behaviors that go along with that, but chicks nowadays don’t like to be told what to do, so it has devolved to simply being a chick-controlled party.
Also, a wedding is not for the wedders; it is really for their parents. It’s THEIR day.