What you're seeing in the East Wing is normal turnover, and what you're seeing in the West Wing is abnormal. It's an aberration to have a team stay as long as this one has.
Win or lose, he realized that it was going to be very difficult to govern and that the better part of valor was to step aside.
There's a tendency after you win your second term to think you're invulnerable. You're not just king of the mountain, you've mastered the mountain. That can often lead to mistakes of excessive pride.