According to the Metro UK Mannequins’ breasts are growing to cater for the number of women who now have plastic surgery (or men’s increased fondness for gigantic boobs). Shop mannequins with 40″ DD breasts are now being used. Given that breast augmentation surgery has increased by 700 per cent in America in the past 10 years this is no longer a niche market.
One thing to note is that instead of being designed for naturally big-breasted women the mannequins’ breasts are abnormally high up for their size suggesting they are modelled on women with implants (and/or designed my a man).
h/t: Spin Thicket