Plenty of water in white adipose tissue. If you've already eaten more than you need to, lipids can just go right to WAT, along with carbs and protein a little while afterwards. I also think the elasticity of WAT should be considered too. Think of a stretched out water balloon. Once it's stretched, it's easy to stretch out. And when it's rigid, it's tougher to stretch out.
Of course that few day binge will come off pretty easy, but it's just crazy how the body works... I like staying lean because when I do binge, it can come off without very much difficulty unless I let it sit there and really solidify. I don't have all the right scientific explanations for it, but let a pot of rendered down fat sit for a few days and look at how hard it is. If it's heated up, different story.
When you diet down on high amounts of androgens, beta-2 stimulants and GH you really fuck the shit out of WAT and make it tough to get fat again. That's why when I diet, I like to diet really hard so it's tough to plump up again. That's been my observations at least. People's bodies are different and there are so many variables. Maybe I'm wrong as well... I don't know lol