Mainly because of "Yongle Dadian".
The "Yongle Dadian" was compiled during the Yongle period of the Ming Dynasty. It is an unprecedented collection of Chinese classics compiled by Yao Guangxiao and the chief minister Xie Jin. It is a collection of Chinese encyclopedia-style documents, with a total volume of 22,937 Volumes (the catalog accounts for 60 volumes), 11,095 volumes, about 370 million words, a collection of 7,000 to 8,000 ancient and modern books, showing the glorious achievements of ancient Chinese scientific culture.
After the "Yongle Dadian" was re-recorded during the Jiajing period of the Ming Dynasty, records about the Dadian are rare, especially the whereabouts of the original Yongle edition is even more confusing. The copy of Yongle also suffered a catastrophe, and most of them died in the war. Today, only more than 800 volumes remain and are scattered around the world. Some people believe that the original version of the ceremony was destroyed by war or fire and has long since disappeared. However, some people believe that the original copy of "Yongle Dadian" may exist in Zhu Di's Changling Tomb, so they planned to excavate Changling after the founding of the People's Republic of China.
Since the tomb passage of Changling could not be found, the Dingling Tomb of Wanli was discovered first. Due to the lack of awareness of cultural relic protection at that time and the specific historical period at that time, the bones and coffins of the Wanli Emperor and the two queens were destroyed, and the large amount of silk fabrics unearthed from Dingling were not effectively protected. Therefore, the excavation of Dingling is also considered to be the first step in the history of archaeology. A great tragedy. Therefore, all active excavations of imperial tombs were stopped.