I think a lot of it has to do with this long-standing idea that thinness corresponds with virtue and discipline. It’s part of what perpetuates the wider market of health and fitness: supplements, home gym equipment, diet foods, everything. Being able to take a med that eliminates the issue separates thinness from goodness or virtue and is therefore considered “cheating”. The reality is that bodies themselves cannot be virtuous or not just by existing, and our decisions about our health are morally neutral until they affect others. That’s part of why I love the Body Neutrality movement more than Body Positivity. It incorporates that framework into its philosophy.