I suspect it’s very hard to not be overweight when so much of the food on offer is stuffed full of sugar and fat, and so many jobs require us to sit down all day. There’s very little in the framework of day to day life these days which makes it easy to be healthy. It’s a massive effort to stay healthy IMO.
That said, if you look at the choices a lot of people are making about what they eat, how much physical movement they build into their daily routine, and how little exercise they do, you do have to wonder if we’ve somehow lost some intelligence at some point in the 20th century!
However, it’s not helpful to make massive generalisations about how people become fat. I suspect a lot of times it’s just lack of time/education to make the decisions needed to live healthily. Sometimes it’s probably lack of self-respect, sometimes it’s probably laziness but overall I suspect it’s really far more complex than laziness.
In this instance it strikes me the doctor was too young to realise that being judgemental isn’t very helpful in solving people’s problems… maybe the fault is mainly in his training which didn’t teach him not to judge… or maybe he was just an insensitive twit!