If you don't need your period to have effective birth control then it seems pointless but:

What does the Pope have to do with placebo pills in your birth control pack?

Yep, you read that right. John Rock, one of the scientists who developed the birth control pill in the 1950s, was a devout Catholic who was eager to earn his pill the approval of the Catholic church. He thought it might appease the Pope if the pill mimicked a woman’s natural menstrual cycle and also figured the placebo week might make it easier for Catholics to practice the rhythm method, which was the Church’s only approved form of birth control at the time. Unfortunately for Rock, the placebo week did not garner the Pope’s approval. The Catholic Church maintained its strong position against birth control, with Pope Paul VI even releasing a statement in 1968 calling birth control “intrinsically wrong.” After John Rock’s placebo campaign failed, he stopped practicing Catholicism, bitterly disappointed that the Pope had not embraced the pill, but the format of birth control pills never changed.