Why don't catwalk models smile?

SOURCE

You'd think that modelling such beautiful designer clothes and unlimited exposure would be enough to put a grin on every successful model's face.
However,take a look at any model beating a determined path down the catwalk and you' d think someone had just told them they would be out of a job much faster than they realise.
What it is, is that the catwalk is suddenly becoming a much more serious place these days and designers feel that when a models shows emotion, their clients notice her more than the clothes. And lets not forget,at the end of the day, fashion is a business. Designers are in the business of selling clothes.
And there we were,thinking the models were frowning because of the many ice creams they have to forgo to remain skinny.