Randomness abound in nature!
Who doesn't like looking at ocean waves, a flowing river, a burning fire or tree leaves moving in the wind? I bet you have spent some time looking at one of those things for longer than you thought, sweetly idling away.I know I love looking at them and other similar phenomena such as falling snow flakes or patterns of rain drops in the puddles.
The keyword here is patterns. They are what I think my brain is looking for when doing it. Our brains have specialized in finding patterns in visual stimuli and love any visual input where they can search for them. All of the above are infinite generators of chaos and randomness so our brains and visual system seem to enjoy looking at them - maybe so they can get some training? Each wave in the ocean is different from another. Their high-level structure is similar but they're never exactly the same, much like the patterns of falling snowflakes or flickering of fire.
Such thoughtless observation when the visual cortex and its pattern-recognition machinery (which I suspect is like specialized piece of hardware and doesn't require much conscious thought) take over lets our conscious part of the brain relax and take a break from being focused on everyday matters. If that is so, no wonder people enjoy it given that they can take a break from reality and enjoy idling away. It may be kind of a natural high, similar to having sex, doing exercise, playing an instrument or other forms of pleasurable human activity where our instincts or senses take over and we can lose track of time.
Losing sense of time has happened to me many times when improvising on the guitar or piano, not trying to play any specific song but simply picking notes at random or building patterns from them. During such sessions I find I play for much longer than I think and have a totally blank stare and cannot communicate verbally with anyone (so reports my wife who occasionally has to witness those blatant displays of mine of breakdown of basic human skills :-))