They were being punished for being orphans or single mothers, for committing petty crimes, or being perceived as rebellious in some way. Via ABC News:
Ireland’s government oversaw workhouses run by Catholic nuns that once held thousands of women and teenage girls in unpaid labor and usually against their will, a fact-finding report concluded Tuesday, establishing state involvement in the country’s infamous Magdalene Laundries for the first time.
Opposition leaders demanded that Prime Minister Enda Kenny offer an official apology for the state’s failure to enforce labor laws and human rights standards in the 10 Magdalene Laundries, and to pledge to establish a taxpayer-funded compensation program for survivors. The report found that 10,012 women were committed to the workhouses from 1922 to the closure of the last two laundries in 1996.
The government since 2002 has paid more than $1.3 billion to more than 13,000 people who suffered abuse in other Catholic-run workhouses and orphanages but explicitly excluded former Magdalene residents, contending these were privately run institutions with negligible state involvement.