I think the focus on nature might be a byproduct or reaction to modern jobs, technology and creature comforts decreasing the participation people have with the world around them. This makes it easy to want to return to a time (real or not) where people lived harder but more fulfilling lives, with camping and games offering ways to act out this ideal.

Of course a desire for a return to nature is not necessarily "modern", see for example Walden, but I think the degree of disconnect has increased to the point it is harder to ignore for a larger number of people.