Expertise in their core domain does not transfer to other domains and you can be as good with your body as any because of discipline and hard work it doesn't say much about how good you are going to be when the work does not involve your body.
Doesn't work always involve your body? Your brain is a muscle and part of your body, right? Not to mention be healthy plays a huge role in your productivity. Learning how to be discipline and focus is something all professionals of all levels work to get to and maintain. So, if they're able to transition that energy and concentration once out of the sport, it's to no surprise they'll be successful.