1/2A glow engines are inherently noisy, electric motors are inherently quiet. I don't care what the db meter says about prop noise, etc., 1/2A glow engines are the most annoying to the general population. About 15 years ago, one of my Cox TDs was "exhibit A" in a noise complaint that landed in court, [so that is my criminal past unveiled [8D]].
Anyway, enough bragging ...it is understandable as to why 1/2A glow got excluded from the PPP. I don't see it as a selfish or subversive act.
It was simply more expedient to make the program electric only.