Why does your doctors when recommending a low carb diet recommend 40g or less each meal. when doctor like dr stephen phinney, dr dom dagostino, dr simon bakker, and and and...that actually works with low carb diet daily, suggest less then 20g a day?

There are degrees: of low carbs. Atkin's diet recommends differing amounts of carbohydrate depending on phase you are in of nutrition plan. A person eating around 2000-calories per day might eat around 225 to 325 carb grams per day (at 45 to 60% carbs/day). Even intake of 120 mg of carbs per day will help to accelerate weight loss. See: https://www.healthline.com/nutrition/how-many-carbs-per-day-to-lose-weight