Not fair. There are multiple reasons for packing on the pounds in an environment of "sufficient food" and for some of those reasons (including medical) it takes a major effort to keep it off.
And that's before you get into genetics...
While there are hereditary factors (i.e. Manute Bol didn't have the same genetic makeup as Oprah), people too often quote "junk science" about metabolism and other processes as an excuse for obesity.
The Metabolism Myth There's no biologic reason to get fatter as you grow older
Moreover, the cases where hormone disorders are the cause of obesity is rare. There are some cases where hormones those related to the thyroid, adrenal glands, pituitary glands, etc are the cause of obesity, but not very often compared to the number of obese Americans.
The #1 Cause of Obesity is Overeating, and overeating the wrong foods.
Period.