As humans, for most of our existence, we lived in nature.
It was our home, where every tree with countless leaves produces the air we breathe, grows nutritious fruits in a rich variety of tastes and colors, and provides shade and shelter from rain and heat.
Our dependence on nature is self-evident, similar to that which defines a healthy relationship of a child with his mother, unconditionally fulfilling his basic needs, and providing him with comfort and a sense of security.
Maintaining this connection has been critical for our survival, and so, over evolutionary timescales, natural selection designed our brains for a strong attachment. The wiring of our sensory systems is molded to recognize meaningful objects in the natural environment, and our emotional systems are developed to attribute a sense of awe, beauty, and comfort when in its presence.