Because we don't all have money to burn mate.
Except that isn't the point - in this case with the expected depreciation it would be cheaper to buy the car thats almost 3 years newer... for just £2400 more. You'll also get 3 years manufacturers warranty etc as well.
How can it possibly make sense to pay so close to new price for a car thats almost 3 years old? I don't get it
