celebrity photographs get shown because they give a look into the thinking of the celebrity, not because the celebrities are great photographers.
What this means is they may get one show, but after that their work will stand or fall on its own merits. Ms. Lange may or may not build a reputation as a photographer if she works at it. I haven't seen her work.
Some do achieve the best of both worlds -- Jeff Bridges is darn good with a widelux, for example, but he makes no claims at being a famous photographer, just an actor who is good at his hobby.