Why is the Wei, Jin, Southern and Northern Dynasties the most important period in the history of calligraphy?

During this period, China's calligraphy has undergone historic changes, and Zhong You changed official script into regular script. Different calligraphy styles, such as Weibei, appeared in all ethnic groups, until various calligraphy styles were continuously blended, forming a new calligraphy style, which also promoted the development of calligraphy in later generations to a higher level. And a large number of famous works in this period have also become the blueprint for calligraphy lovers to learn. Therefore, calligraphy in this period is undoubtedly crucial to the whole history of calligraphy!