Because before now, I had always heard that the show was a huge disappointment and finished nearly last in the ratings every year.
NBC committed to the show for three seasons. A program as expensive as Star Trek
wouldn't have stayed on the air for the sixteen episodes NBC initially orered if it had been "nearly last in the the ratings." (One of Star Trek
's time slot competitors, The Tammy Grimes Show
, was cancelled after just four episodes which weren't even that