It's because doctors have only given generic diet advice. It's easy to say 'eat healthy and lose some weight, do some exercise' but they rarely gave specifics. Mostly this is because their clientele would have freaked out if told they need to eat less than a third of their current diet, but the doctors still failed a little there. To be fair, doctors have only recently started recommending 'keto' or low-carb diets to type 1s as well. Hell, my doctor still hasn't. The closest I ever got was this real fatass of a doctor who needed to take his own advice, who said 50% of a plate should be vegetables, 25% lean meat, and 25% carbs. He said stay away from potatoes, corn, sweet potatoes, and beets because of their high glycemic index, but never recommended overall lowering of carb intake or counting of calories. I don't know of a single diabetic who wouldn't benefit from lowering their carb (sugar) intake, and thus their intake of insulin. Some of my other comments here went into those a bit deeper.