In NASCAR, as in other forms of motorsport, spectator interest has been on the wane for many years, and those in authority are trying to do something about it.
A place such as Bristol Motor Speedway - only half a mile in length, but one of the signature tracks - used 10 or 15 years ago to be full to the rafters, but these days its amphitheatre stands, expanded to meet apparently unlimited demand, look forlorn on race days, and even the Daytona 500 pulls nothing like the crowds it did.
In Formula 1 it's been the same story. Silverstone might be invariably a sell-out, but it's far from typical, and in part this is due to the changing map of the world championship.