They are implicitly admitting that obesity is bad. By insisting that they are not promoting obesity and merely "living their lives," they are denying promoting obesity because of course that would be as bad as promoting anorexia. It's funny because they could simply take the position that all people regardless of sickness can be promoted and happy and then their claim would at least be internally consistent. But they can't stand sharing the spotlight with other people, and they can't admit that obesity is also a sickness, so they build these arbitrary walls to omit anorexics so only fats get to be special.