Answer:
Because there was a need to expedite the arrival of products to Beijing and the quickest way to do that was to extend the Grand Canal there.
Step-by-step explanation:
As Beijing was the city with the highest concentration of people, in addition to being a commercial, cultural and scientific center, it was necessary that communication between Beijing and other areas of China be very fast, especially in relation to the quantity of products, such as grains, which were produced outside Beijing, but which were in great demand in Beijing.
The fastest and most efficient form of transport at the time was through the Grand Canal, for which reason the emperor decided to connect other channels to the Grand Canal, allowing it to extend as far as Beijing.