I would bet before the invention of and proliferation of ARf's, a beginner would spend alot of time constructing his first trainer. As a result he would want to spend his time getting the most out of it. Also, with the purchase of his second plane the time spent in construction would allow for him to acquire a skill level equal to his second plane. With ARF's you could crank out a new one each week.

I also was inspired by my local hobby shop owner. According to him there is an amazing number of planes that used to be used as trainers in the old days or are just as easy to fly as a trainer.

Just my thought and personal experience.