Guess I didn't think it through. They would have to import the crude they refine (there is no oil there) and export by-products and any excess gasoline. Cheaper to import the gas rather than refine it, I suppose.
IIRC there are two refineries in Hawaii, basically right next to each other over by Barbers Point Oahu.
Guess the remaining one will have less competition. That’ll help lower prices. /s