Yeah I admit I'm kind of baffled by the attitude they seemed to have towards that. Surely they must have seen the importance of having the characters act consistently from episode to episode, and in having a set of established rules for this world to exist in.
You get the sense they saw the Enterprise as being just another generic spaceship, with a bunch of generic officers who only existed to serve the story they came up with. I don't think a lot of them really understood the kind of extensive world-building Roddenberry was attempting to do with this show.
I get that sense with some of the writers, others not so much. George Clayton Johnson, for example, had some interesting ideas that Roddenberry's re-write of 'The Man Trap' gutted.