First, Emperor Taizong admired calligraphy very much. What a country wants to prosper depends mainly on whether the contemporary monarch likes it or not in ancient times. Calligraphy, for example, was a favorite of Emperor Taizong. Tang Taizong believed that calligraphy was an art, and it was also an art that all courtiers should have. Once upon a time, there was an official named Chu Suiliang in the imperial court. He was a little-known political official before, and later he was favored by Emperor Taizong because of his good handwriting, which shows how much he valued calligraphy in the eyes of Emperor Taizong.
Second, calligraphers in the Tang Dynasty were a profession. Why was calligraphy so popular in the Tang Dynasty? In fact, in the Tang Dynasty, calligraphers were a profession. Buddhism was very popular in the Tang Dynasty. Therefore, many ancient temples need a good writer to copy scriptures. Therefore, many calligraphers copied scriptures for a living. At that time, people in the Tang Dynasty needed calligraphers for weddings and funerals. For example, when a person dies, a monument needs to be erected.
Emperor Taizong's admiration for calligraphy gave many calligraphers living space at that time, such as Yan Zhenqing and Liu Gongquan. In other dynasties, there may not be such a big room for development, but in the Tang Dynasty, it was completely different. They can write their own calligraphy schools and develop their own calligraphy skills.