In the case of Motability the biggest factor is the VAT free purchase, basically a 20% discount. This advantage is eroded as the car gets older and its value declines. Brand new its value is greater than its purchase price. This is why after 3 years as the cars value decreases and service/repair cost increase, the cost of leasing the car generally does not fall, and the AP is calculated on a 3 year depreciation, not 5.