Serious answer. I'd speculate that being fat is a way of life. Ok, it's not like bodybuilding which is apparently a "lifestyle" to some in which the end goal is to look good, but fatness is a consequence of a lot of shit (yes, overconsumption and lack of exercise obviously).
I bet a lot of it comes from family though. It's pretty rare to see a family of fatties with one person in good shape. Same with friends. You hardly ever see a really fit person hanging out with an obese group, or a married couple with one into fitness and the other one really out of shape. If you were fat and that was your world, fat family, fat friends, fat spouse, I bet you'd actually get ostracised to some degree for losing weight and getting fit.
Nutritional ignorance certainly plays a big part. That's why Jenny Craig and Weightwatchers make so much money. People who don't understand nutrition see "diet food" as some magical mystery. The notion that a given volume of lettuce contains less calories than that volume of beans, or that volume of beef, or that volume of ice cream, is totally lost on them. Their upbringing and exposure to nutritional knowledge (lack thereof) plays a part, but laziness or a belief that they'll never understand the mystery of nutrition means they never make an effort to learn.
Weight loss advertisements do more harm than good. Fatties see them and think they're going to look like a cover model in 10 weeks. When they see hardly any progress (how much different are you going to look at 40% than 42%) they give up. Approaching fat loss with a result oriented attitude is counterproductive. Fat goes on slow, fat comes off slow, but you're not going to make a lot of money running a weight loss company by telling people the truth.
And some people are just lazy for whatever reason. Some have a sense of hopelessness that they can't overcome, some have psych triggers that make them reach for junk food at the drop of a hat, some are scared of failure since they view getting in shape as a win or lose situation, and some are just delusional as hell and think they are such wonderful human beings that everyone should love them no matter how fat they get. Having witnessed more than a few of these types asking for advice, claiming they're on a diet while munching on a king-sized Butterfinger (in spite of the diabetes!!), I have to conclude that some of them are just plain insane.