Being thin is a social status object, so cheating to increase social status by using drugs, is treated negatively, and because it is then a false social status due to drugs, it is considered worse than not losing the weight?
The logic of human social status related behaviour is intrinsically disturbing. And built into our brains at a deep level.
The worst part , is not the general public or even family members having open or not so visible bigotry, but the medical profession, which has always treated obese persons badly, and I would guess it is partly they are just as bigoted as everyone else, and partly the fact that they could not treat the problem, so tended to find it extra frustrating. I think medical attitudes will slowly improve now there are drugs that work, but very few patients who could benefit from GLP's get them suggested by doctors, when up to half the population might be helped by them.