Because Chu's pen is easy to master. The inscriptions circulated are also very clear and exquisite.
Yu Shinan's will do Yu and Chu were four schools of thought in the early Tang Dynasty. They were contemporary and had similar statutes.
Zhao Mengfu was born in the late Yuan Dynasty and early Yuan Dynasty. His regular script is close to running script and he writes quickly. According to historical records, Zhao has a saying that it is difficult for beginners to master.