This is a part, a big part, of why they have always worn habits, along with monks attire and priests. They all have distinctive dress for a reason. These religious orders are not jobs, they are vocations. You don't do nunning, you are a nun. It is a whole life dedicated to God, and it is a recognition of who you really are. To think that you could be a nun or priest in the afternoon, take off your uniform and be someone else like you were getting off your shift at Taco Bell is a completely alien concept.
So when you see these new nuns in civilian clothes, the natural question is to ask is are they really nuns? And the answer, especially from experience since the 1960s, is that the clothes make the woman.