Yeah, Kasey had a real bad experience with physical exhaustion and dehydration at the 2017 Brickyard 400, which he won. Seemed to have more susceptibility to that earlier this year, and after the Southern 500 Labor Day weekend, sat out the Brickyard 400 this year. And still sitting out races since then. Your health is all you have, if you don't have that, well...
He's set financially. I suspect deep inside, he doesn't want to be an also ran with less financially capable teams that can't throw money at things to get that extra 1/100 of a percent out of the car.
Good choice for Kasey, wasn't a fan in terms of a favorite driver to follow, but good on him.