I would not want to think that all 'overweight' people have an eating disorder (just as all 'thin' people don't).
However, when we express sympathy with eating disorders, it is almost always those people with anorexia / bulimia, and not those who are overweight.
There are a lot of reasons that people may become overweight, many rooted in childhood. I know many people cannot understand why someone would become more than just a little overweight.
There is a narrative that many kind people try to understand, and which gets lots of publicity, about various addictions, gambling & alcoholism. I hear little sympathy directed at those whose issues result in them becoming overweight.
When I was a health visitor, I dealt with some children who were 'overweight' because of metabolic disorders, kidney disease, some complex syndromes. Some health workers as well as families had difficulty in grasping the reasons for excess weight gain, not realising that it was not simply overeating.