This may be related to feng shui. People in China pay attention to good luck. The Terracotta Warriors and Horses of Qin Shihuang's Mausoleum are, to put it bluntly, funerary objects, which are heavy in yin and are not suitable for taking pictures. Just like visiting the Ming Tombs, try not to take a group photo.
Of course, if you believe such a thing, you don't. If there are no taboos in this respect, you don't need to consider so much.