A backlog of 1300 cars is only about 10-20 trains of grain. Some coal trains regularly run 100 cars. The problem is loading/unloading and getting the empties back to the right place.
This is the reason for the backlog. Like lumber cars, they do not pick up 100 cars all at the same place. They may pick up four from one grain elevator, ten from the next, 18 from the next. These all get consolidated into one train. Its like the milk run. Then they may go to a gate way point like Minneapolis and split off from there.
This is why the railroads like oil and coal trains. All 100 cars start at the same place and go to the same place. It is a very efficient use of their equipment and train crews.