There are two reasons. First, we know that most people don't make any enlargements, much less giant Bruce-size ones. They make their livings selling big enlargements, so it makes sense for them to be more concerned about grain and to use slower films. This type of lens lets in much more light. Now, let's return to where you should set up for an action shot of the race.
Corners are where a lot of maneuvering takes place.
It's where the action happens. If it's a tough corner, cars have to slow dramatically entering the corner, and then accelerate out of it. You have to analyze the course and decide which part of the action in the corner is likely to yield the most exciting photographs. Realize that there's a lot going on in each corner. They make a great subject for your camera.