The concept of fat being the problem is a little confused. Body fat, ie subcutaneous, is not actually a problem as such, it causes strain on joints, and the cardiovascular system if there is enough of it. It has no bearing on diabetes, the problem there is Ectopic fat. The fat around and within the organs. Once this Ectopic fat has gone, the rest has no effect on diabetes. so an individual could be carrying 120lb of excess fat, but only perhaps 10 to 12lb is having an effect. this is why remission figures are reached long before any substantial weight loss is achieved.
This explains very fat non diabetics, the fat is subcutaneous, and not causing a diabetic problem.
The very low calorie shake approach has 2 goals, first and probably least, is to get patients into remission. The second and most likely, most important, is to make money, so if patients keep returning again is a big plus.