The average person doesn't buy a Denali and take it off-roading where they need low range.
AWD system if far better to drive, far safer on a paved or snow packed road. It is moving power around to the wheels that need it giving you the best possible traction at all times. On dry pavement in the summer it is moving power to give you the best fuel economy.
Say your wife is driving her Denali, safe with AWD on a snow packed road, but when she gets into town and is parking it she doesn't have to deal with the front end locking and making it hard to turn the wheels, lock to lock while parking. It lets the inside will slip to make it easy to navigate. Nothing to push, nothing to shift in or out of, all automatic.
Driving it hard on a paved surface the power transfers forward before the rear wheels lose traction.