There are loads of reasons, one though can be because not all fat people sit around eating crappy food 24/7? I'm on the smaller end of obese (going by BMI) and that's only 'cause I've been on a diet for the past 9 months barely eating anything. Yet you think all fat people just sit around lazily eating fast food and costing the NHS loads? There's a difference between morbidly obese unable to walk and needed healthcare and just 'fat'. I know loads of fat people, and I don't think any of them actually cause any strain to the NHS or anything (which from experience, on here tends to be the main reason people claim obesity is bad).
If they are really bad to the point where it's massively damaging their health, then be concerned and offer to help them, isn't that what people do to alcoholics drug abusers etc? They go to therapy, they aren't shamed. Okay they're looked down upon but I think only people who have a problem should actually even be compared to them. Most fat people don't have a problem, they just were either raised that way (raised by fat people eating large portions to became fat as they grew up) or eat a bit more and it just builds up over time. Same with thin people, not all of them have anorexia, many are just naturally slim or maybe don't eat enough/eat enough but burn it off quickly, yet they don't get shamed the way fat people do. (Really thin people get shamed though, I will admit, but the slightly underweight ones don't, unlike even overweight people who are immediately judged as lazy people who always eat).
It's so annoying people thinking that ALL fat people just sit around eating all the time, they really don't from what I've experienced.