[haleycookie]

Because there is no definitive proof grain free is the main and only cause at this point.
The reason to avoid carbs (grains and potatoes, peas, etc) is because dogs are facilitative carnivores. Meaning they can eat a small amount of carb but it’s not really necessary. So meat based diets are the most healthy. Meat based foods will be rated higher on this site for that reason.
I would consider 20lbs+ over small breed requirements.
Some Boston’s are quite small and would fall into that category. I’m sure at the end of the day if you feed a proper diet “smallbreed” or not won’t matter much. Just feed the correct amount of calories for your dogs ideal weight and you’ll be fine. “Senior”, “small breed” , “healthy weight”, etc are gimmick words for the most part to charge high prices for a “special” food when in reality senior foods have such a small amount of glucosamine it’s not even close enough to be effective, small breed foods typically are just smaller kibble, and weight loss foods are foods where meat is taken out and replaced with a carb, not the best idea for a carnivore looking to loose weight lol.