Why did China's ancient calligraphy enter the conscious stage from spontaneity after Wei and Jin Dynasties?

Official script, seal script and bronze inscriptions before Wei and Jin Dynasties. Just a tool function. In Wei and Jin Dynasties, regular script appeared on the basis of simplifying official script, and gradually developed and popularized. Zhong Qin, Mrs Wei, Wang Xizhi, Wang Xianzhi and other outstanding regular script writers appeared. Since then, from Jin to Southern and Northern Dynasties, from Sui to Tang Dynasty. Further standardize, point, horizontal, vertical, skimming, pressing and hooking six strokes to finalize the design. Wei and Jin dynasties began to be calligraphers who not only used functions, but also had independent aesthetic and artistic forms and consciously wrote.