Why Seabiscuit did not run the Triple Crown?

The Kentucky Derby, the first race of the Triple Crown is just for 3 year olds. At the time that Seabiscuit was a 3 year old he was disappointing his trainers which would eventually lead him to be sold for the bottom price of several thousand dollars.When he was sole the new buyers bought him a companion named Pumpkin and his jockey was Red Paulard.Seabiscuit and Red were a toast and jam match.