Why? Because labor at the dealership is nearly $200/hour, that's why.
I will be hard pressed to buy anything with more than 4 cylinders ever again. Even my wife's Kia SUV is a 2.4L 4-banger (love that engine though! Wish it was in my car!). It gets the job done and you can reach everything when you pop the hood. I always say, you know a car is too complex when you can't look down into the engine compartment and see a single square inch of the driveway.