First, the political and economic center of the Qin Dynasty was mainly in the north, and Handan and Daliang in the Yellow River valley were close to Xianyang, Qin Dynasty, and there was no big river connecting them. Road transportation was the main mode of transportation, and water transportation didn't play a big role at that time.

Second, the arrival of a peaceful environment and the lack of military logistics transportation are also the reasons for the decline of grain transportation. After Qin unified the whole country, Lingqu was excavated mainly to conquer Baiyue. With the end of the war, logistics and military supplies are reduced, and food transportation is also much less.

Three, the decline of a mode of transportation, there must be the rise of other modes of transportation. After Qin unified the whole country, Qin Shihuang built a large number of galloping roads (equivalent to the current expressways) throughout the country. Compared with the slow delivery of grain, galloping has become the choice of many people.

At that time, the population was not very large, and the food supply could basically meet the local demand, so there was no need to transport food across regions. Moreover, local economic ties are not very close, and there are few exchanges.