Why didn't anybody ever think of this before?

Interesting plot. Hollywood can screw up a soup sandwich.

They kinda did in an episode of the Super Friends

Gulliver's Gigantic Goof

Dr. Gulliver uses his micro-wave reducer to shrink every adult human being in the world down to an economical, convenient size of 2" tall. He will remain full-sized to rule and watch over the mini population of the world.