I don’t follow celebrity stories at all, so I am interpreting from the far outside. I would have to say that if they’ve chosen to part at this stage of their lives, there’s been a deepening distance for a very long time, deep enough that they can’t even agree that they may as well stick it out now and take care of each other in their old age. They want freedom from each other even more than they want companionship, comfort, and security in their senior years. If that’s the case, the feelings must be very strong, and they’re better off apart.
I’d go further and guess that they waited longer than they would have if he hadn’t been a runner for the White House. I’d say they waited until it was certain that that was never going to happen.
One of my favorite “News of the Weird” stories from many years ago was that of the 93-year-old woman who divorced her husband after sixty-some years of marriage, saying in disgust that she had given up hope he was ever going to change.