Stay with me.
Look, my point is that we(humans) must have some innate need to justify our decisions, especially to a random audience who undoubtedly thinks we are crazy. So it seems that trying to explain our own decisions, especially when we feel so far from the norm, is ubiquitous because I see it in almost every adventure movie I watch.
I, of course, am not pardoned from this type of thought. Here is one explanation for why we go into the wild:
By 1964, two research laboratories proved that the morphology and chemistry or physiology of the brain could be experientially altered (Bennett et al. 1964, Hubel and Wiesel 1965).
This is true of mammals of any age. Okay, so what? Basically the way that our brain looks and functions on a physical level can be altered by the environment that we are in. As we live in a highly autonomous and affluent society, we have choices as to what environment we immerse ourself in. So if we have the choice, what environment should we live in? Darwin speculated that the reason why wild rabbits had larger brains than domestic rats is that they lived in an "enriched" environment: the wild.
So the wild is an enriched environment and the environment can have an impact on the morphology, physiology, and chemistry of the brain. Therefor people that go to the wild are actually increasing the functionality of their minds by being in an enriched environment.
I don't want anyone to read too far into this line of reasoning. I am not claiming that kayakers are necessarily intelligent. I am just suggesting that being in the wild is a rich environment and anyone that is exposed to that must feel the power of the wild and be drawn to it as an enriching experience. It is addicting, the problem solving involved with navigating a canyon, the sights, smells, sounds, and social dynamics create mindful environments that invigorate the mind and body in ways that other situations cannot.
Kayakers and all other adventurers must be aware of this, and probably feel bored and unengaged by the city life because of its relatively austere feel. I can say from personal experience that solving problems in a small group during rescue situations, portages, and scouts are incredibly enriching, satisfying, and engaging experiences. It is hard to create that same type of environment in any urban situation because it is the safety of all involved that is on the line when in the wild. I just don't derive as much satisfaction when discussing learning objectives from algebra I, or how far apart to plant the beans. Those things are satisfying, but just not as dynamic.
So this is my first stab at explaining why we do it; we are actually physically altering our minds by being out there.
Get out there and alter your mind.