I watched the Live press conference at 10am. He gave 3 reasons:
1) He was satisfied with his career and ran at his best, with the best, and was a contender
2) He wants to focus on other interests (people and ambitions) in his life that the NASCAR grind does not allow room for.....He mentioned farming, flying, and politics - thought the politics was an interest because of his passion for freedom that was raised by a media guy
3) His helath is excellent and so is his families health. He did say NASCAR is an inherently dangerous sport and he'd like to be healthy 30 years from now.
He has no plans and described it as jumping not into another life raft but just jumping out into the air. He said the 3 primary reasons noted above told his gut that now is the time. He handled it with class.
He also mentioned that Dale Jr's head injury got his attention (and his wife is a neurologist) so given that he has two young kids and enough money to do what he wants he will not suffer at all.
I quit working a great paying job and stayed unemployed for more than a year because one day I raised my head up and realized I was on an endless treadmill doing what I didn't enjoy.... I cleared the fog and have been doing some of my best work since.....sometimes you just gotta clear your mind.
He will not be the last in the near future and if someone gets seriously injured or killed it will likely accelerate.