Overblown weddings are a consequence of the propensity of late twentieth and early twenty first Americans to over-consume material goods in general.
There are two general ways to approach this. Keep late twentieth century and early twenty first century American culture intact, but it doesn't affect weddings. The way this happens is that the move away from traditional values in the 1960s is greater and more permanent than IOTL so that most people, including couples with children, just stop getting married. Those that do have formal weddings are religious people out of touch with mainstream culture and they keep their church weddings simple.
In this timeline, the money that is spent on weddings still gets spent, it just gets spent on something more ridiculous.
Alternatively, you can stop the consumer culture and the wedding aspect goes away, but this has big effects. You can do anything in this regard from going back to the colonial period to tinker with the culture, stop or change the New Deal so consumer spending is not the way to get out of the Great Depression, keeping the USA out of World Wars I and II so the US does not become the great superpower (plus keeping the USA out of World War I or preventing it probably also prevents the Great Depression in the first place, as well as the "roaring 20s"), stop the Baby Boom from happening, which stopping US participation in World War 2 accomplishes, or for a last minute POD the more anti-materialist aspects of the culture culture of the 1970s gain more traction and are not reversed.