A cousin of my was a multiple-tour forward observer for the U.S. Army in the Korean War. He spent a lot of time doing extended hiking after that.
I'm not sure if it was a result of his experience in Korea, but I get the impression he really wanted some extended alone time. I never asked because I didn't want to risk dragging him into some terrible memories.
It's a fairly popular activity for people in the military to get engaged in, for many reasons. Particularly people who were deployed in the field.
The back country is an environment where one is able to apply physical skills and tools, earned over years of experience, and to which most civilians attribute no value. The solitude is nice, however I think most veterans actually prefer company on activities like this, there just aren't many people who can cope with the mileage or the off-the-grid aspects.
I've never been in the military myself, but I'm a reasonably experienced backpacker. Discussions on the subject have made friends out of many coworkers, who had been deployed in the field while serving in the military.
You should ask your cousin about it, maybe even ask if you can join him sometime; he'd probably actually really enjoy you expressing an interest and wanting to tag along.
I'm not sure if it was a result of his experience in Korea, but I get the impression he really wanted some extended alone time. I never asked because I didn't want to risk dragging him into some terrible memories.