Why is the Shanghai-Kunming Expressway from Shanghai to Jiangxi blocked every day?

There are two main reasons for traffic jams from Shanghai to Jiangxi on the Shanghai-Kunming Expressway every day:

First of all, the Shanghai-Kunming Expressway is the main artery of the national horizontal expressway. From Shanghai to Kunming, it passes through important prefecture-level cities in many provinces, and many vehicles pass by every year, especially large trucks. This road is also the main road of traffic, and there are many large trucks. Once there are more large trucks, it is easy to collide with small cars, which leads to traffic jams much more frequently than other high-speed vehicles.

Secondly, according to the map, the traffic volume in Jiangxi province of Shanghai-Kunming Expressway is very large, and the intersections of expressways are often closed, resulting in traffic jams.