You are right. My theory is that most models are using their bodies to advertise clothes, so the bodies have to look decent enough (plain) to market the clothes but not sexy enough to be NSFW if the image is displayed publicly. So secondary sexual characteristics are toned down (most models are stick then and flat as a board).
The bit that's wrong in the instructions, is that suspenders should be worn underneath a thong.
That way you can gently remove the thong when you are about to fuck, whilst leaving the suspenders on.
That's why I love it so much when I see a woman with the thong worn over the suspenders, it means she's dressing not just for show, but for action!