People are fat because they enjoy eating and don't enjoy exercising.
I also believe that Crisco is to blame for most of the weight/health issues in the world circa 1911. The introduction of hydrogenated oils, which is a man made oil that is the equivalent to edible plastic (it was used to make candles before it was realized it could be used in food as a cheap substitute that also acted as a preservative). The human body takes longer to break it down and since it is a foreign substance it latches itself onto various parts of the body (other then the stomach) giving you pouches in the neck, under the arms, etc.
I've been reading ingredients since learning of this oil and if I see the words Hydrogenated I don't buy it.
Here is the wiki article on it... interesting/scary stuff.