The blog 1964 has an article about why young women are attracted to a religious order. The author, Nicole Cornell attributes the attraction to be community. I see what she's saying. I agree with a codicil. First, (and which Ms. Cornell probably just takes for granted), is that the young lady has to be in love. That's madly in love with Jesus. She has to be so in love that she wants nothing else except to get as close to Jesus as she can. She wants to spend her life with Him.
Next, she looks around to find like minded people. She can't help but notice nuns in habit. So she approaches them. It's that simple. Why would she approach a religious sister who doesn't wear a habit? How would she know that that lady was a religious sister?
Even if somehow someone told her that certain people dressed like regular people were religious sisters, why would she want to become a religious that looked like, and acted like, and worked just like, a Lay Dominican, a Secular Franciscan, a Third Order Carmelite, etc.?