I think part of its appeal for some (not all, certainly, but some) fans was the fact its production was deeply chronicled in David Gerrold's "behind the scenes" book. It allowed that first generation of viewers to vicariously become part of the backstage production, at least from the writer's perspective.
Since 1973, a LOT of development anecdotes have been revealed, but in the early 70s, it was the only material besides Whitfield's "Making of Star Trek" that gave us any idea what it was like creating that series.
Sincerely,
Bill
That's a good point. I actually read Gerrold's book before I ever got the chance to see the episode (the late-90s VHS tape re-releases hadn't gotten around the Tribbles yet at the time I principally became a Star Trek fan

