It has a lot to do with prestige and geography. California is one of the few places in the U.S. that has an optimal climate for winemaking. Oregon, Washington, and even New York (blurgh) have wineries but they don't have the climate or culture to compete against California the way California can compare to European fine wines. Because of this, it means that a lot of the U.S. "good wine" comes from one state, and not only one state, but often specific areas in this state (Napa Valley, Sonoma County, Santa Cruz, etc.) which shoots up the price because capitalism and because yes, Cali is very much "teh ghey" also.