Different drivers react differently to; having a car fast enough to win a World Championship, closing in on a World Championship, winning a World Championship, post World Championship, post a second or third World Championship etc.
25 years experience of developing the vehicle performance of F1 cars and as part of this process assessing driver performance variations. Both in racing and testing.
For the sake of clarity, I will modify my statement to, based on my experience, it is extremely unlikely to be anything to do with the car.