Why was Reuben Smith disengaged from work and then reappointed in Anna Sewell's Black Beauty?

At the beginning of Part 2, Chapter 25 of Anna Sewell's Black Beauty, the title character, who is the narrator and protagonist, explains the story of Reuben Smith.Reuben Smith was a groom at Earlshall. Black Beauty describes him as being an excellent groom; he was kind, gentle, and even as knowledgeable in horse care as a veterinarian. Yet, Smith also had a problem with alcoholism. Black Beauty explains that he wasn't...

At the beginning of Part 2, Chapter 25 of Anna Sewell's Black Beauty, the title character, who is the narrator and protagonist, explains the story of Reuben Smith.

Reuben Smith was a groom at Earlshall. Black Beauty describes him as being an excellent groom; he was kind, gentle, and even as knowledgeable in horse care as a veterinarian. Yet, Smith also had a problem with alcoholism. Black Beauty explains that he wasn't constantly a drunkard like most alcoholics, but instead, after weeks or months of soberness, he would "have a 'bout' of it ... and be a disgrace to himself, a terror to his wife, and a nuisance to all that had to do with him." It was while he was drunk that he became hazardous to the horses. Since he was such a good groom and his drunken bouts happened relatively infrequently, York, the head coachman, was willing to keep him on and keep his ailment a secret from the earl. However, one night Smith was so drunk he was unable to drive a group of ladies and gentlemen home from a party, and a "gentleman of the party had to mount the box and drive the ladies home" himself. York was unable to keep this particularly unfortunate incident a secret from the earl, and the earl promptly fired Smith.

However, Black Beauty further explains that just before he and Ginger were sold to the earl, Smith was forgiven and hired again. The earl was a "very kind-hearted" person, and York, still convinced of Smith's general goodness of character and of his excellent abilities as a groom, was able to convince the earl to forgive Smith and rehire him, so long as Smith promised "he would never taste another drop" (Ch. 25).

However, sadly, when York leaves for London and is replaced by Smith, Smith missteps and again gets drunk. This time, his drunken bout causes an accident that leads to the death of himself and the ruination of Black Beauty's knees.