1. Historically being fat was considered a sign of good health. Of course, this was during times of massive food scarcity and the definition of fat was probably very different from what we consider fat today.
2. Massive amounts of money involved in telling people to eat/drink more, and then spend more money in gyms and taking pills to lose that weight. As opposed to just eating less and then living normal healthy active lives. There’s not much money in the latter.
3. People wanting to stop fat-shaming (which is also unequivocally bad…fat shaming only makes it harder for people to lose weight), trying to convince other people that someone being fat does not make them bad, quickly morphing into being fat is good.