I always find it funny that after Spock and McCoy get back to the library, the three of them take their time in leaving. I remember Scotty is telling Kirk that it is now or never, I am beaming you up anyway. The planet is about to be destroyed and Scotty is going to defy Kirk to get him back. There is a real sense that the planet is going to be destroyed right now. Then Kirk, Spock and McCoy have their special moment talking about Spock's great love now being dead. Get off the planet guys, you can talk about Zarabeth when you get back to the Enterprise.
They weren't about to spend money for filming on the ship for 5 lines of dialogue. There were zero ship interior shots in that episode.