Why are there so many simplified characters in Yan Zhenqing?

The national writing policy also requires the writing and popularization of simplified characters, and a large part of simplified characters in Yan Zhenqing directly inherited ancient folk characters. The view that calligraphy creation can only write traditional Chinese characters is generally recognized by calligraphy circles, but in the era of simplified Chinese characters, this view has many loopholes. One is that there are simplified characters in ancient classic inscriptions and ancient books, and the other is that the national writing policy also requires writing and popularizing simplified characters. Therefore, how to deal with simplified characters in calligraphy is a very complicated topic.