That would mean adding a couple more years of payments. Or he could turn the car in and go find something else. Probably another lease. And he'd join the ranks of those who will always be driving new, but expensive cars. Maybe Mark is concerned with the reliability of a four year old car.
Most cars can give more than four years of dependable service.
Besides the ownership issue, a lease could set Mark up for a nasty surprise. Sure, he expects to drive the car for four years. But everything doesn't always go according to plan. A lost job or sick child could make that car payment too big to handle. If he should need to get out of the deal early, it's harder to terminate a lease.