Real life history of the tropeDespite what many believe, flight attendants in Real Life are primarily there to save your life, not to pour you coffee or look sexy. The number one factor determining whether passengers actually survive a "survivable" accident is the response of the flight attendants. Indeed, this trope evolved almost entirely by accident: the first flight attendants were male, as they were considered analogous to the (male) ship's steward on oceangoing vessels. One woman, a pilot and Registered Nurse named Ellen Church, approached United Airlines in 1929 to be a pilot, but was turned down (they were only hiring male pilots); however, she also suggested to United that they hire Registered Nurses (a virtually all-female profession at the time) as stewards. Church argued that having a medical professional on board would help with passengers' fear of flying, as would having it be a woman—and indeed, most airlines had found that when the male stewards gave safety instructions, they panicked.
When United hired Church as a stewardess—the first female flight attendant ever—the suits were pleased with the lack of panic, and hired more "flying nurses"—being an RN was more or less required to be a flight attendant in North America until World War II sucked up the supply of available nurses. The good looks typically associated with the stewardesses of mid-century America also had a practical origin: the stewardess had to be short (because of the cramped spaces in early aircraft), slim (to reduce weight and save fuel), and physically at peak health (to minimize the risk that this key employee wouldn't be incapacitated mid-flight). The service elements, besides being inherited from the seagoing position of steward, were in part to distract passengers from the fear that they might die before arriving at their destinations.
Eventually, the Jet Age caused all the practical problems that created the trope to disappear, so (in the US at least) when flight attendants who had been fired for gaining weight or getting married or having children sued the airlines, the courts agreed with them that there was no longer a bona fide reason that all flight attendants had to be petite women in the prime of youth, and the profession was opened up to all (but flight attendants, whether male or female, are all still trained in, among other things, flight safety procedures and first aid).