Because of the high level of knowledge, skill, and detail required to accomplish something which on the surface appears to be easy. For example, look at what makes the Dreamliner fly safely, transporting hundreds of passengers to their destinations. See also Hoover's speech about engineers.
I've never heard that before.
yea me neither
Because people don't really see the Engineers at work. Your average man on the street doesn't think where the electricity comes from when he flips the switch, or how the water gets to his toilet when he pulls the handle or, for that matter, where does it go after the flush.
In the minds of most people the highways and buildings just magically spring into being, the latest gadgets magically appear on the shelves of electronic stores, and the Internet works because Al Gore blurted out that he gave it to us during the 2000 presidential election campaign.