Because Ford USA is stupid....
And I'll just post now and say that if any dimwitted fu(k-knuckle comes on here and says it's based off a Taurus or Contour or any other Ford. I will personally come over your house and snap off a steaming log on your kitchen counter!
EDIT: With the 300C, Magnum and Pontiac GTO (nee Holden Monaro) here in the states, Ford might pull their proverbial thumbs out of their asses and bring the Falcon over to combatt the new segment in the market: Full Size RWD Passenger Cars.
Please don't even bring up the Crown Vic, that thing is a shrimp-boat/death-trap and a sad piece of engineering to boot.