Millions of people have been imprisoned for just solely Marijuana, you don't think the US basically saying they are wrong is a huge cultural event?
It is not one of the biggest cultural changes. There have been changes that literally touched every living person's life in profound ways. It is a notable change, and a good change. But not one of the biggest. This is specially the case since weed is already legalized, decriminalized, or at least ignored in a lot of places.