It’s my understanding also that for much of the 20th century, as Petra and Gertabelle said, joining a religious order was a way for a single woman to do meaningful work in the world while having opportunities in areas like nursing, teaching, social work etc basically provided for her, and while also having a supportive community so she wouldn’t be all alone/ on her own. A single lay woman pursuing a career in those days instead of getting married would likely run into a lot of opposition from family and society, would probably not have a supportive environment, might lead a very lonely life (or be vulnerable to all kinds of harm from men), and also the religious dimension was lacking.
Since the 1970s, single women are now able to have good jobs and careers without needing to join a religious order. I have read that nowadays, the women who join religious orders tend to be more interested in the spiritual dimensions, like prayer and contemplation, and are not looking so much to work out in the world as the past generations of women religious.
