That’s a good question. They’re incredible handy on R/C cars and other little odds & ends. I used mine awhile back working with tiny little nuts and screws in a collection of vintage bubble gum machines I bought at an estate sale.
Perhaps their primary use was for working on “ignitions”, and overtime people have worked less on ignitions and more on other things with them, so calling them midget wrenches sounded like a better fit? That’s just my opinion of what happened.
I’m curious to also know if anyone has a real answer.