The truth is, most models have small boobs, and a womens naturally shaped boobs are normal and attractive. Bras don’t look good under clothing, and most small chested women are far more attractive without them.

Breasts are just another part of the human body and they’re nothing to be ashamed of. There are many communities all around the world where women can go topless.
Women showing their breasts in an art show (yes, fashion is art) isn’t shocking. It’s like going into an art museum and being appalled at all the nudes. The center of the fashion world is the wealthy and they are really not interested in middle-class morality, which is generally religion/superstition-driven and shame-driven.
One of the biggest trends this year has been for models to ditch bras and flash their nipples on the catwalk
Also, quite often female models don’t wear undergarments. Bra and panty lines are not pretty. They might be visible under the clothing, either because of the cut or material used. and if exposed, the undergarment itself could distract from the clothing being modeled.
Designers sometimes need to project and exaggerate. Glamour and sex appeal to a confident and sophisticated customer sells. But on the runway, sex sells.
Fashion houses have been pushing the boundaries of taste, decency, propriety and legality in order to draw attention to their creations and sell their products. On the runway, the volume is turned up. Nipples are visible, blazers are worn over bras, models wear tops but no bottoms.