Everything that needs fixing looks like a nail.
People with diabetes mellitus are issued with blood glucose meters - and nothing else.
For people with type 1 diabetes, that's fine. They lack insulin, so they have to inject insulin in the right amounts & types to keep their blood glucose levels within reasonable limits. Applying Bernstein's Law of small numbers by reducing glycaemic load to a minimum keeps blood glucose levels within reasonable limits (between 3 & 7mmol/L) most of the time. See also The problem with Diabetes.
For people with type 2 diabetes and excessive visceral (belly) fat (~85% of people with type 2 diabetes), that's not fine. Their disease is a disease of chronic excess fuel intake relative to fuel oxidation, causing dyseverythingaemia (hyperglycaemia, hypercholesterolaemia, hypoHDL-cholesterolaemia, hyperNEFAaemia, hypertriglyceridaemia, hyperuricaemia, etc). People who have type 2 diabetes don't have only postprandial hyperglycaemia - they also have postprandial hypertriglyceridaemia. See Postprandial lipoprotein clearance in type 2 diabetes: fenofibrate effects.
However, because the only tool in their box is a blood glucose meter, their disease looks like a disease of only hyperglycaemia. Applying Bernstein's Law of small numbers by reducing carbohydrate intake to a minimum keeps blood glucose levels within reasonable limits, but makes everything else worse if energy from carbohydrates is replaced by energy from fats.
Only if energy from carbohydrates is reduced AND energy from fats isn't increased to compensate (i.e. eat a LCLF PSMF or Modified PSMF), does carbohydrate restriction help people with type 2 diabetes.