Because they can't make a profit selling it here. Plus, the government taxes the @#$% out of diesel, which is what this car runs on. It's still oil-based, but it's "clean diesel."
Ford opted not to sell it here b/c there was no market for it. It's too expensive, and diesel fuel is MORE expensive than octane-based gasoline.
They did a lot of market research before coming to that decision. Remember, Obama's plan to "tax big oil" is part of the reason you can't drive a 65 mpg American car here!! Those diesel taxes are paying off!!! (/sarcasm off)