While we tend to think that overeating leads to obesity, the author proposes that we are overeating because we are getting fat due to other environmental factors.
When calories are stored in fat tissue, they cannot be used by the rest of the body. If all your calories are being stored, your body doesn't have enough calories to carry out its basic functions, and it craves more.
It is analogous to edema, a condition in which fluid leaks from blood vessels into surrounding tissues. People with edema can never quench their thirst because water doesn't stay where the body needs it. Similarly, people whose bodies are really good at storing fat are never satiated because they don't have enough calories circulating throughout their body.
I think this is great way to simplify what's biologically happening with insulin, ghrelin, etc. when it comes to hunger, satiety, and fat storage.