Why is the living room floor of Zeng Guofan's former residence soil?

The living room floor of Zeng Guofan's former residence is earth, which keeps its original appearance.

One of the four famous ministers in the late Qing Dynasty, the Han nationality, whose first name was Zicheng, whose word was Bohan, whose name was Di Sheng, lived in the seventieth grandson of Saint Ceng Zi, was a modern politician, strategist, philosopher, writer, founder and commander-in-chief of the Xiang Army in China.

Bai Yutang, the birthplace of Zeng Guofan, is the first former residence. It is located at the foot of Gaogu Mountain in Tianping Village, Heye Town, kilometers away from Fuhoutang. On November 26th, 1811, the 16th year of Jiaqing, Zeng Guofan was born here.