Don't you think happy people sell more clothes?
Some say Fashion models don't smile because they need to create a sense of distance between themselves and the observer.
Its adding to the sales pitch of attraction, those kinds of people look mysterious and reserved. Like they dont give a fuck.
Gary Gedall, psychologist, actor and a trained professional model, gave two reasons on Quora on why models don't smile
The first, and the least valid, is that it is incredibly difficult to smile when you are stressed, and walking on a catwalk, trying to remember all the stuff that you are supposed to do, is not a 'cake-walk'.
The second reason is to do with the 'story' that the director / designer wishes to portray, each show has to make its mark as interesting and different. There has been and there are fashion shows, usually for spring collections, where the atmosphere is light, friendly and smiley.
However, to create a dramatic effect, the models have to convey the energy of the theme of the show, and dramatic rarely rhymes, with smiles.
The logic is that people want to be excited, intrigued, taken by the show, hence, excited, intrigued and taken by the models.
A sweet smile is nice, but a scowl can be attractive.
A pretty face or smile takes our attention in the moment, but a beautiful woman, (that is to say with stronger characteristics / make up / look), we will remember for some time.
However, all the Victoria Secret models - they are quite smiley. Whatever the designer feel would convey the tone of the collection.