I can't say that I agree with that. All the advertisements I see, where the face is visible, the model is smiling. Or laughing. Or some facial expression to denote happiness.
I think for some styles, it's supposed to look sultry and sexy, but usually ends up as a sneering scowl as if the woman has no time for the photographer or the designer (?) of the clothes... which she probably doesn't, despite the money.
I have seen far more fashion and other advertising photos whose models are smiling.
"A smile is the best make-up any girl can wear" - Marilyn Monroe.
Source: a transfer left on my lounge wall by the home's previous owner. I like it so much I keep it!