In many places, they already are. If you are skinny and have a disability, it's more "invisible". Even with MRIs showing that you got some fucked up shit going on inside, people look at you and think you look normal. It's even worse when you want to work, or force yourself to work part time, or go to the gym or be somewhat active. But be a blob of fat, sitting on your ever expanding ass all day, not moving and making your issue even worse through your inaction? Well you must be reeeeeely disabled. Even though the issue would be greatly improved by, you know, not having a body that resembles a melting pile of ice cream.