For the 10th time rewriting this reply:

I have been really struggling to understand this phenomenon. I now, think I could make an argument for psychological awareness and responsibility. This is possibly one of the most scarce combination of resources in existence. I will make the case from experience struggling with my weight since I was about 7 years old. I would agree with most in this thread that it's an addiction, but one that can NEVER go away completely. Survival requires eating, but does not require drugs/alcohol. I say this from experience being around all kinds of addicts, friends/family, the symptoms are nearly identical. Some of these people had heart attacks, liver failures, kidney failures and still refuse to change their lifestyles. The just get their surgery, take their prescribed pills for the rest of their life and keep going. I would argue it's shares social-cultural attributes most closely to casual alcoholism(if that's even a thing), but with more acceptance. Example: It's easy to tell people I'm sober, it's a a lot more difficult to tell people I'm "ex-fat" and get the same support. 

You could throw a stone in just about any direction and hit a possible cause. So want to stay in my lane.