I am not really sure they are trying to look sexy. I think they are just being silly. They appear to be mocking the standard “sexy pose” of models and wannabees web porn stars.
It’s like these pictures of white teenage girls who pucker and pout their lips and make gang signs with their hands.
I may be wrong but that's my perception.
I guess I'm from the wrong generation. I've always thought that subtleties were worlds away more sexy than in your face posing.