Acording to the athour why is beauty smith the way he is

Beauty Smith was a coward. He could not be powerful among humans, so he chose to take power in his excessive abuse of animals.

For Beauty Smith was cruel in the way that cowards are cruel.  Cringing and snivelling himself before the blows or angry speech of a man, he revenged himself, in turn, upon creatures weaker than he.  All life likes power, and Beauty Smith was no exception.  Denied the expression of power amongst his own kind, he fell back upon the lesser creatures and there vindicated the life that was in him.