Might I offer my take on why few people take on the adventure of pilot training? Visibility.
I simply don't think GA enters into the mind of the average youngster. Beyond commercial aviation, by which I mean the airliners ferrying them from one major location to another, I don't think they have any real concept of what GA is and that they might in fact be able to take to the skies without years of study and uniform.
GA is pretty hidden. I only came to notice it when switching jobs which involved me designing Flight Simulators! Now I'm training for my PPL.