Well having the limited refining capacity we have making 96 different types of fuel to meet state and Federal "clean air" standards for summer driving might have something to do with it
Nobody in his right mind would build a new refinery in the USA. Nobody. It simply is not going to happen. Expansions, maybe, but only if they have a good ROI and quick payback. Most US refinery investment lately has gone into environmental projects that reformulate gasoline and desulfurize diesel.