Read this excerpt from the call of the wild.

a scotch half-breed took charge of him and his mates, and in company with a dozen other dog-teams he started back over the weary trail to dawson. it was no light running now, nor record time, but heavy toil each day, with a heavy load behind; for this was the mail train, carrying word from the world to the men who sought gold under the shadow of the pole.

the third-person-omniscient point of view readers understand this excerpt in a way that they wouldn’t if buck were the narrator because it

provides details about the time of day that cannot be described from a first-person point of view.
provides details about buck’s experiences that cannot be described from a first-person point of view.
gives readers details about buck’s thoughts and feelings that they might not otherwise know.
gives readers details about the historical context that they might not otherwise know.