I wonder how many know Gene Roddenberry, the creator, had been a FE (I believe) with Pan Am, flying some of the longest routes at the time.
While he went into science fiction and some things not necessarily possible (like traveling faster than the speed of light), he kept it realistic. Unlike other science fiction, it was primarily focused on human (and half Vulcan) emotions and interactions, in a science fiction setting. That is part of the enduring appeal of the franchise.