My father-in-law used to run one of those shows in the late 60s. He was the president of the Ruritan Club and the show was an annual fundraiser. It was held in a flattish field, the club members put up temporary fence and built the jumps (four around the outside, rails and a coop), and there were classes like egg and spoon and plantation hack in addition to the more recognizable pony and working hunters. There were proper printed programs in which local businesses purchased ad space (I have a few saved from his files after he died!) and the show was apparently popular and profitable.
The event was even covered in the local newspaper.
But it would never fly today. Trainers and exhibitors expect the same footing and jumps and year end award prizes that you get at a rated show, just in a one day format and at a fraction of the cost. They want the show manager to be a professional horseman who knows the rule book, not a dairy farmer who was the president of the Ruritans.