Granted I have never raced a road course, but this is the difference I see in the two. I gather that most road courses are basically racer-funded at the amateur level. If you want to have a track day or race, the money comes from the racers. Using Harris Hill, MSR, and Hallett as examples, they do not have grandstand seating, where circle tracks usually have quite large grandstands. Basically, the road race is for the driver, while the circle track is for the driver AND the fan. There is some admission and concession income there that is not generated by the road course. Regardless as to whether that's profit, it's at least cash-flow.
That being said, I'm definitely not complaining about these payouts. My class races for $75/car. Just pointing out what I see.