It’s actually harder (requires more advanced technology) to refine heavy and sour crude. The US refining industry process this type of oil mainly because it’s more profitable not because of some limitation.

American oil on the other hand (As in extracted out of the ground) is actually too high quality for domestic consumption therefore gets shipped overseas and sold at a premium. The weird economics of this are made possible by globalization. While it’s not fungible on a dime it’s easy to solve and the US really does hold all the cards when it comes to the petroleum industry.