Yes, because to get the 40g of Protein out of Tuna you have to also have X amount of Fat Grams and other stuff.

WHEY Protein avoids that, it basically gives you Protein and nothing/not much else. At the expense of not tasting well.

You can always go with a meal supplement that has more calories and fat and stuff in it, as well as the Protein, *and* tastes good.

Problem with those, they cost more and they have the Calories/Fat that you might not want, although a lot of people love them.