But every woman who is dieting and exercising to get a so-called beach body, they do probably want one just like that woman.
The product is trying to sell the idea that you can have that body if you drink their shakes.
If they advertised it with a picture of ordinary women in bikinis, nobody would buy it, there would be nothing to aim for. So using that picture is right for them, it makes sense.
The idea that only women who look like that are considered attractive might be something you disagree with, but the company wants to sell product, not change society's ideas about attractiveness.
The idea that using shakes can make you healthy or thin might be something you disagree with, but that's your business, you aren't their market in that case, they want to sell to (perhaps) more gullible and insecure adults, and it's their right to do so.
Like mamapants, I don't understand what the problem is that people would complain about. A bikini company might use a picture of a bigger woman in a bikini in their advert, or a sun tan lotion company, but a company selling diet products is obviously going to sell them using someone slim.
A company doesn't have to have morals. You can't complain because they don't create adverts that tie in with your personal world view and try to make the world a better place. Well you can, but you won't get anywhere, because it's IMO nonsense to do so.