I didn't reaolize she chose to leave... I agree she was painful to watch but I feel her character was getting better ... slightly.
She was so pleased by the lines written for her in "Skin of Evil" that she said, "If all the scripts were this good, I never would have left".
To be fair to Denise Crosby, she must have been
incredibly disappointed that her promised role didn't materialize. Like the introduction of the MACOs in "Enterprise", Yar was supposed to have been in charge of Away Teams. When Riker took away teams down to a new planet, Yar was supposed to be doing all the orders and security strategizing, but, as written, she was mostly delivering the hackneyed "Hailing frequencies open" lines that Uhura had done in TOS.
A little off topic but why did Gates (Dr. Crusher) leave for one season was it planned was she prego?
Gates McFadden didn't find out she was pregnant until after doing her own stuntwork in "Remember Me", IIRC. She then had to disguise her pregnancy with longer and longer lab coats.
Supposedly, Gene Roddenberry was displeased with the development of Crusher in Season One. Beverly and (the female) Lesley Crusher were essentially creations of David Gerrold, who'd already had a major falling out with GR, and no one - except Patrick Stewart and Gates McFadden - was all that impressed with the mutual romantic interest subplot. One of Crusher's best episodes would have been Gerrold's "Blood and Fire", which was canned.
It was decided not to renew McFadden's contract. I recall Richard Arnold saying at a convention at the time that the producers felt that Crusher had become "a whiner" and, to complicate matters, the actress's red hair refused to hold its style under the hot lights and she was constantly being sent back to Hairdressing to have her hair washed and reset to match continuity. Dr Crusher was costing the production time and money, and it was causing much friction on the set, in addition to arguments about the Picard/Crusher dynamic.
Additionally, McFadden has since said there was some sexual(?) harrassment from someone high up on the production team. She clashed with Maurice Hurley, and there was pressure to have the character replaced. Eventually, GR pushed to have his old friend Diana Muldaur come in to play a female version of McCoy. Tracy Torme had pushed for an
alien doctor, hence the appearance of Selar in Season Two.
When Muldaur (who did not have the standard five-year contract), said she'd be unavailable for the first four episodes of Season Three (to star in "The Return of McCloud" reunion telemovie), it was realised the most efficient way to resolve the problem was to bring back McFadden - Maurice Hurley had already departed - and they bought in a selection of different, very expensive, red wigs, thus resolving another problem that had caused the most annoying of the production delays surround the Crusher character in Season One.