(Source: Motion Picture Classic)
Vampy Makeup Was Supposed To Mimic Vampires
Women had something of a gender liberation during the '20s, where they no longer wanted to be confined to the stereotypical "parlor ornament" roles that their mothers had. They were newly independent, working, educated women, which meant that — for the first time ever— they had agency. 

This directly translated into "vampy" makeup. Vamp was short for vampire, and the idea was that women wanted to turn themselves into femme fatales, where they used men on a whim, sucked their bank accounts dry, and moved onto the next victim once they grew bored. It was both an exercise in sexual freedom, and seen as a rightful punishment for men who had used and abused women for centuries prior.