Well, Delta did buy a refinery last year. It was a crazy move but I haven't heard much about how it's going since then.
Emirates gets huge subsidies because its a goal of Dubai to become a world air hub. It certainly makes sense for them given their geographical position but I don't see how US carriers are supposed to compete with that.
Perhaps the UAE(/European/applicable foreign) governments should start charging US carriers an extra fee to combat the subsidies when they land abroad.
I'm sure no-one would complain about that or attempt to use the US government's muscle to fight it...