I don't find it odd in the least, most of my career has been centered around mechanical things. It has paid the bills and provided moments of interest and I got good at each facet I tried but I am so flipping tired of things with engines that when I change careers again I don't even want to own a car or drive anymore. Engines, cars, machines, and the industries around them have never been my calling, just my day job.
So I can easily see HCB being in a similar boat, he found a good way to make a living, rode that wave, and paid the bills for many years.
I can also understand that once his retirement account was full, that he could and would move on to/back to something he enjoyed more. Actually the craft that he originally trained for before entering photography.