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.

Fake numbers, but I have heard it is something like the US produces 100 units of light crude -exports it all, and imports 50 units of heavy. Net exporter, but the stuff we use domestically for gas refineries comes from elsewhere.

Technically, the refineries can be retooled to take a different blend, but it is expensive to do.

US crude oil is exported to foreign refineries for blending purposes. By blending low-quality crude with high-quality crude it can reduce the total costs to the refiner even after accounting for the fact that you had to buy high-quality crude to improve the properties of the domestic crude.