It was an added level of enticement that the women were allowed into the private rooms of Achashverosh, much like a presidential affair in the Oval Office, or Nebuchadnetzer’s defiling a prostitute in the Holy Temple. According to the Midrash (Esther Rabba 3:10), Vashti needed to utilize vaster space for her party so that the women would not be in close quarters, thus going through their menses at the same time. This guaranteed that at least some of the women would be available to gratify the men’s baser urges.