Why are there so many seals on celebrity calligraphy and painting?

This is a testimony that ancient calligraphy works can be passed down to this day. Every seal is a collector who has collected this work, and most collectors with seals have a history to check, which is one of the important means for us to judge the authenticity of ancient calligraphy works (not to mention fraud); At the same time, it also proves that it is orderly circulating. The seal covers of these seals are in harmony with calligraphy works, which further improves their appreciation. The seal is originally a token, which plays the role of verification. After the Song and Yuan Dynasties, it was used by literati in calligraphy and painting works, forming a book seal that set each other off and became interesting, and it has been passed down to this day. So most of the seals were stamped after the Song and Yuan Dynasties. It's not the author's.