You’re right, and I’m not completely sure on the reason why eating disorders that cause weight gain aren’t given enough focus.
Perhaps it’s because many people generally think of overeating as something that a person should be able to control, rather than an actual disorder or illness. Society teaches us that fat people are fat because they are lazy, gluttonous, and unable to stop eating. That way of thinking would make it hard for people to comprehend that first of all, some fat people are fat because they’re normal fucking people and fat bodies exist naturally - but some do have actual eating disorders.
It’s all about perception and what a person is willing to understand. I’d love to know more about this.