I don't know. I just think that killing your friend's only child is something you can't come back from.
Even with episodic TV.
Its really shocking. Too shocking.
And maybe that's why they didn't go for it (although it was not so much "killing" as being accidentally responsible for her death). But with '60s TV you never know. It's easy for modern viewers to fail to realize how dedicated '60s TV producers were to keeping each episode independent. Back then, the classiest dramas were anthologies, so that's what TV producers aspired to. The main reasons they bothered with continuing characters and situations at all were economic: having a regular cast created viewer loyalty and boosted ratings, and reusing sets, costumes, stock footage, etc. was cheaper than having to build new stuff every week.
^ Chris all of what you are saying makes sense but the episode they came up with is considered one of the worst of the original series.
The one has nothing to do with the other. You asked why they decided to drop the McCoy's-daughter angle and I offered a couple of possible explanations for what their thinking was. I wasn't saying I agreed with their thinking; I was just trying to imagine what it might have been.
I am not saying a plot line where Chekov was in love with McCoy's daughter would necessarily have produced great drama but you would have been giving back story to a main character who basically had none (McCoy) and at least connecting him to another character on the ship who could always use more screentime ( Chekov)
But that wasn't their priority. Again, I'm not defending or endorsing their choices, just describing them. But Spock was the runaway star of TOS, the one that the network wanted the show to focus on the most. Somebody involved in the production probably thought something like, "Hey, the kids like Spock because he's this alienated outsider type like them, so let's do a story about Spock grooving with space hippies because the kids'll go for that and we'll get good ratings." I'm not saying that was a better decision creatively
than focusing on McCoy -- it strikes me as mercenary and somewhat shallow -- but by the same token, it's not really that difficult to understand why they made the choice.
After all, this wasn't the first time this happened. "This Side of Paradise" was going to be a Sulu romance, but it was rewritten for Spock. And the tendency toward Spock-centrism was particularly strong in the third season -- e.g. "Spectre of the Gun" where Spock's the one giving all the historical exposition about Tombstone even though Kirk or McCoy would've been the more logical choice, or "Spock's Brain" where they were saddled with the remote-controlled Spock zombie as an excuse to keep Nimoy on camera for more of the episode.