US refineries are highly configurable and can refine any crude. They make more money refining difficult crude because they have the capability to handle it and many refineries do not, so naturally they prefer it for profitability reasons. The difference is extra refining steps that can be bypassed if they are not needed. Processing light sweet crude means some of their capital assets are sitting idle because they aren’t needed.

The US also exports its own crude for blending with other crude at foreign refineries. A refinery may not be able to process some types of crude but can process that crude if blended with a different type of crude to change its average properties. The limit to this for refineries is the cost of buying and shipping enough suitable blending crude to the refinery.