Maybe the authors needed to give characters access to machines in a setting with no technological market.
Maybe the authors were inspired by the sheer number of inventors that lived in the Industrial Revolution, like Thomas Edison, Robert Fulton, Nikola Tesla, Charles Babbage and George Stephenson.
Maybe it's the Rule of Cool.
Whatever the reason, at least one Gadgeteer Genius or Mad Scientist is usually a part of the main cast of any Steampunk or Gaslamp Fantasy. Very commonly, inventors, mad scientists, mechanics, gadgeteers, and other masters of technology and Magitek are scattered throughout the story like candy on Halloween night.
Note: if there's only one Gadgeteer Genius or Mad Scientist in a work, it's not this trope. If, however, there is a relatively high ratio of tech experts to normal people, then it falls under this trope.
- Arcanum: Of Steamworks & Magick Obscura
- Professor Layton and the Curious Village technically counts, since of the five real human beings in the cast, three - Layton, Don Paolo and Bruno - are canonically Gadgeteer Geniuses.
- World of Warcraft has two entire races, gnomes and goblins, with this as their exclusive "hat".