I would say it is the "health aspect", but........I have Xrays that say otherwise. Though I am down sixtyish pounds in two years.
Really it is about freedom for me. Being out in the woods makes me feel more free than I can describe. Even when I am hammering it I have a sense of calm.
Another dimension of that is that we spend so much time being responsible, for work, our kids, our spouses. That sometimes I just want to be a kid playing in the dirt. Being 10 years old and running over stuff and going fast and hitting stuff...How cool is that?!