The best explanation for why artists often do not want their work photographed, even if there is no flash, is A) They do not want others copying or imitating their arts.
Photographs of artwork can easily be replicated and shared, which can lead to unauthorized reproductions or forgeries. By limiting the number of photographs of their work, artists can maintain a level of control over their art and prevent it from being copied without their permission. Additionally, artists may want their work to be seen in person to fully appreciate the details and nuances that may not be captured in a photograph.
I hope this helped!
~~~Harsha~~~