It borders on luxury SUV territory. If you compare it to its "lesser" GM siblings (Traverse and Outlook) you'll see it has more "bling" on the exterior, and also comes with more standard equipment.
As for being more expensive than the Tiguan. You can't really compare the two directly because the Acadia is much larger, the Tiguan is a compact crossover and competes more with the GMC Terrain and Chevrolet Equinox. It kinda makes sense that a Tiguan is half the price of the Acadia, it's about half the size of the Acadia.
I think a more fair question is why is the Tiguan so expensive relative to its competition (Chevy Equinox, GMC Terrain, etc)?
public demand on the targeted income of the buyers, that's why when you by them second hand or off lease. There 68% less then what they went for off the lot.