An average in this case is a misleading statistic. Not all classes have the same number of events. There are two or three events that are way above average (for example - Madcatter for 16s, NACs for all classes) that skew the average.

There remain several locations where Tigers are raced OD in significant numbers - upstate NY and the Pacific NW are the biggest two. In those areas, they constitute a much larger percentage of attendees, but when you spread it out over the whole of North America, then they are only 6%.