John Cannon not in all episodes + a limited role

Popularity with viewers, I suspect. Being the more colorful characters, Buck and Manolito kind of took over the airtime.

Buck and Manolito were the most popular characters. I loved the hot Linda Cristal ( Victoria) best of all. What made those characters work is they marched to their own drummers. Victoria and Manolito did not do what their father Don Sebestian wanted and Buck was on Confederate side of the Civil War while John was on the Union. Of course, both Don Sebestian and John were strong and powerful men who could intimidate almost anyone but those characters (see John's first wife compared to Victoria as an example of this). But they were also extremely loyal: Victoria to John and Buck and Manolito to Victoria. Characters who remain true to themselves ( instead of being fake), and being loyal are what work well.