Why can't these tracks run an open show? No ROC or sanctioning body involved, just show up and race
Although I agree with you, I think the "die was cast" a number of years ago, that would prevent that from happening. Many years ago, there were indeed 2 classes of cars, late models and modifieds. And the rules, as few as there were, were pretty uniform across the region. And there were a large number of cars in the area, so te individual tracks/promoters never worried about drawing a good field.
As the cars, especially the modifieds, became more specialized, and more importantly, much more expensive, the promoters did two things. They first began instituting rules like tire and gear rules, in an effort to cut expense costs. While somewhat successful, the costs still escalated, so they then wrote even more rules, which brought on the "sport mod" or "B-mod", which while well intentioned, really diluted the field of cars. And another intention of some of these rules was to keep the cars "legal" for one track only, in a promoter's effort to keep the field full at HIS track, other tracks be damned.
And to run an "open show", as you suggested, could potentially still not draw a really big field, because in order to get ALL the "modifieds" out for a show, would potentially require the drivers/owners to make modifications that wouldn't be practical for 1-2 races in a season.
Just my $0.02 worth......