Why did......

Well, she had a lot of costumes to play roles in and I think the blue dress was a symbol of her playing Chyna Blue, so she would wear the same dress all the time.

It's basically the illustration of her character. Yes, she makes good money, but that obviously goes out the window at night when she goes to the seedy downtown motel and dresses in an overly worn outfit to get out her insecurities.

Come on, her "China Blue" look is one of the only good thing in this bizarre movie.