Nichelle Nichols had an issue with her character
It should come as no surprise by now that some of the actors from Star Trek: The Original Series had difficulties with how little time their characters were given onscreen or how the lines were divvied up when the scripts were finished. In fact, there have been ongoing feuds about egos and the like that have been going on since the series ended in 1969. Some of it might have come from having a different understanding of how the show was going to work. That is how Nichelle Nichols saw it.
According to a quote from Nichols, published in The Fifty Year Mission The First 25 Years by Edward Gross and Mark A. Altman [p.166], initially, the series and all of the films were supposed to be about an ensemble cast, the stars of which were going to be given equal time onscreen. She said at some point William Shatner and Leonard Nimoy were separated from the rest of the cast, essentially being chosen as the stars. NIchols wasn’t happy with how that panned out.
Nichelle Nichols didn’t mind not being the star of Star Trek
What the actress did have a problem with was being typecast as her character and yet, playing a role with so little to do onscreen. As essentially the only female lead once Grace Lee Whitney’s time on the show was over, Nichols spent most of her time in the chair at the communications console, telling Captain Kirk the progress of the hailing frequencies.
Perhaps the production team made the decision to focus on a smaller number of characters because it was easier. With seven cast members, including Whitney, it would have been a lot of work to give everyone maximum coverage every episode. That said, an episode or two a season focusing on minor characters might have gone a long way toward easing some of the dissension.
There’s certainly no way to fix this situation, but the Star Trek properties that are airing now can learn from their predecessor to avoid similar dissatisfaction among the cast members.