Well, I know that you are very interested and curious about those celebrities. Anyway, it is true that a lot of them would wear sunglasses wherever they are whenever they are in public. So, from what I know, they do that just because they want some sort of privacy and also , true, try to be more attractive and keep a low profile.
For 3 reasons. First sunglasses can makes them different and cool. Be a celebrity, you have to be unique and special. Second, to avoid paparazzi. Sometimes, celebrities don't want people recognize them, and they want to have a normal life, so they wear sunglasses. Third, to conceal their tired look. Be a celebrity, you have to work very late. And this may cause black eye and so on.
Yes, a lot of celebrities wear sunglasses indoors just for the cool looks. They will show their great personality. The sunglasses can be regarded as the great accessories which will make them look cool. The sunglasses could also be matched with their clothing which will make them look better at the appearance. As we know, this accessory could protect your eyes from the uv rays in the strong sun lights. It becomes the necessary one in the model fashion.