We are talking about the population in generl Monica not those few with a diagnosed disorder.
Most fat people eat too much, and by too much I mean too much for their particular metabolism. My daughter suffers from an underactive thyroid which does not respond well to medication, but she is quite slim because she moderates her diet, quite radically.
But in general people are in denial, and we've heard all these reasons before and, to be frank, most of them are excuses trotted out by those who have no medical conditions. The population is getting fatter and fatter, and NOT because they are suddenly all developing some metabolic disorder.