I don't think the "operator" of the station is really relevant.
The fact is that most if not all the car parks are of a temporary nature (ie fields). If they are saturated, then you're going to end up with a hell of a lot of stuck vehicles. These will no doubt be towed out, but there will probably be some damage to cars. Next thing the organisers will face claims from numerous Insurance Companies etc.
On top of that, once exiting the fields, you then have the problems of muck being dragged onto the public roads, which causes road safety problems.
Folks just have to accept that airfields, stations or bases (take your pick) are by their nature not "set-up" for 100,000 spectators and their vehicles.
Better to cancel today rather than wait until most folks are in queues outside the gates.
Cheers
Stew