Why did Emperor Taizong let Yu Shinan, Chu Suiliang and Feng Chengsu copy the Preface to Lanting?

The first reason must be that these three people are famous for their calligraphy. In addition, it may be because all three of them are bachelors in the Hong Wen Pavilion. According to the compilation of Hong Wen Pavilion in the early Tang Dynasty, it is estimated that there are less than 38 people, all of whom are literati in the Tang Dynasty. It is said that Feng Chengsu's dragon book Preface to Lanting Collection is the closest to the original work.