Why did Emperor Kangxi and Emperor Yongzheng always copy the Heart Sutra by hand?

The cultural policy of the Qing Dynasty was based on the culture of the Central Plains, but in order to manage Tibet and Yunnan, which were vassal regions at that time, it attached great importance to the development of Buddhism. After being exposed to the idea of the unity of Buddhism, Confucianism and Taoism in the Central Plains, many royal families in the Qing Dynasty also studied Confucian culture and believed in Buddhism. One is to better manage Buddhist areas, and the other is to accept Buddhist culture.