I do recall reading somewhere that it may be our natural tendency as humans to be lazy. Thousands of years ago when our ancestors were hunter/gatherers, food was very scarce. People did not have energy to waste on excess activity. Therefore, whenever they were not looking for food, they would be as lazy as possible to preserve energy.

See, laziness isn't bad at all. I'm just doing what my body is programmed to do. Laziness is sweet.