Several reasons IMO for the demise of tracks here in the US.

1. Lack of a development series to feed the pro ranks. MotoAmerica might be a last ditch effort with "Moto3" and "Moto2-like" rules. Remember the RedBull Rookies Cup? Dead. So no impetus to run road races at the same level.

2. Public image of motorcyclists in general. Either bar-hoppin Harleys or squids stunting on freeways.

As for the Miller track itself, it currently runs the Lucas Oil Offroad trucks, ALMS, Pirelli World Challenge races to name a few... again.. how many follow those series vs how many follow NASCRAP?