>>19691385It was just the fashion. There were plenty of women with tits, but they deemphasized them, and the ones with tits were never held up as being at the height of fashionable beauty. In particular, flappers often bound their chests pretty tightly.
Here's Norma Talmadge, a 20s movie star. On the left is her in flapper gear, on the right is her in the 40s. She isn't exactly sporting DDs, but on the right you clearly see that she has some decent-sized boobies, and she didn't spontaneously generate them in the intervening years.
