They do allow photography without flash and that is vigorously pursued. All these pictures and the many others I took where strictly without the use of flash. In many, especially in dark ambience situations they required wide aperture settings together with slow speeds, which often resulted in blurred photos. 

It’s just in some exhibits that the taking of pictures is not allowed, like this particular exhibit. I would generally think that the individual artist would benefit highly when like in this case, their artwork is getting free publicity and exposure (sorry for the pun).