Why did Jim thornton's friends from call of the wild leave him beside the river?

In "The Call of the Wild," Jim Thornton's friends leave him beside the river because they are trying to cross a dangerous and unstable bridge. They believe that Thornton, who is injured and unable to travel quickly, would slow them down and put the group at greater risk. Despite their departure, Thornton's loyalty and bond with his dog Buck remain strong, highlighting themes of companionship and sacrifice.