My understanding is that the basic small 2 stroke engine we call an HT was originally developed by the Russians in the early 1930's to serve as the power source for man-portable military radio systems.
I suspect that the first radioman to carry a 100+ pound radio pack with attached generator and engine figured out he'd be better off with a wheelbarrow, the second one said - "I'll put it on a bicycle rack", and the 3rd one said, "Heck with that, I'll let itr power the bike!"