The terrific Television's New Frontier: The 1960s blog has numerous detailed and informative posts on many of our favorite westerns. Below is the opening paragraph of their post on Bronco. For the full post click on the link at the end...
Though it had hit the top 30 in the Nielsen ratings in its first two seasons, reaching #24 in its 1957-58 debut and inching up to #21 the next season, Sugarfoot was the first of the three rotating Warner Brothers westerns to be canceled, with only 5 episodes airing in 1961, the last on April 17. Even though Bronco (hatched a year after Sugarfoot to combat Clint Walker of Cheyenne in his dispute with the studio's skin-flint practices) never reached the top 30, it was kept around until 1962, the same year that Cheyenne bit the dust. But Warners didn't entirely abandon westerns that year because they also launched a new series, The Dakotas, in the fall of 1962, though it lasted only a single season. So it's unclear exactly why Sugarfoot got the axe when it did.
Without evidence to the contrary, it appears that the decision to cancel the series may have been an impulsive one. Warner Brothers was still employing their crossover scheme of having Bronco's Ty Hardin guest star on Sugarfoot in the third-from-last episode "Angel" on March 6, 1961. The following week Will Hutchins' Tom Brewster character was featured in the Bronco episode "Yankee Tornado." The crossover scheme was intended to lure fans of one series to watch the other series, so if Sugarfoot were on the way out, it makes little sense to have Hutchins appear on Bronco a month before his show was to be canceled. Secondly, the introduction of sidekick wannabe Toothy Thompson in the January 16, 1961 episode of the same name hardly seems like a move for a dying series.
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