That and it's way easier to go from retooling from sour to sweet than reverse, way easier to go from heavy to light than reverse, etc. Not suggesting it's just

That and it's way easier to go from retooling from sour to sweet than reverse, way easier to go from heavy to light than reverse, etc. Not suggesting it's just a flip a switch kind of change, but it's usually a net reduction in complexity in refining for both of those changes.