First of all, the political center of the Sui Dynasty was in the north, and most of the grain was supplied by the Jianghuai area. Relying on land transportation, the traffic flow is small, the speed is slow and the cost is high, which can not meet the needs.
Secondly, after the destruction of the Sui Dynasty, the Sui government also needed to open a North-South Grand Canal in order to strengthen its control over the Northeast and Jiangnan areas. Of course, this canal later became the purpose of Emperor Yang Di's voyage to the West.
Building a canal can be said to be: the disadvantages are temporary and the benefits are in the future.
History is written by winners, and in order to show their glorious image, it will definitely discredit the last dynasty more or less, so
Yang Di can only be a fatuous and dissolute king of national subjugation in the history books.